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Financial Instruments - Schedule of Financial Instruments, Measured at Fair Value on a Recurring and Non-recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents $ 649,916 $ 410,683
Marketable securities 1,805,278 1,558,987
Carrying Amount | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 0  
Carrying Amount | Level 1 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 0  
Derivative liability   0
Carrying Amount | Level 1 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 300,000 127,500
Carrying Amount | Level 1 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 222,713 230,898
Carrying Amount | Level 1 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 69,922 19,967
Carrying Amount | Level 1 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 1 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   0
Carrying Amount | Level 1 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Carrying Amount | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 0  
Carrying Amount | Level 2 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 5,830  
Derivative liability   12,216
Carrying Amount | Level 2 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 2 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 2 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 2 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 1,212,643 1,180,622
Carrying Amount | Level 2 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   4,994
Carrying Amount | Level 2 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 200,000 60,000
Carrying Amount | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 2,500  
Carrying Amount | Level 3 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 0  
Derivative liability   0
Carrying Amount | Level 3 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 3 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 3 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 3 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Carrying Amount | Level 3 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   0
Carrying Amount | Level 3 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Fair Value | Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 0  
Fair Value | Level 1 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 0  
Derivative liability   0
Fair Value | Level 1 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 301,354 128,241
Fair Value | Level 1 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 223,403 231,299
Fair Value | Level 1 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 69,919 19,962
Fair Value | Level 1 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 1 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   0
Fair Value | Level 1 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 0 0
Fair Value | Level 2    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 0  
Fair Value | Level 2 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 5,830  
Derivative liability   12,216
Fair Value | Level 2 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 2 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 2 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 2 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 1,216,822 1,182,437
Fair Value | Level 2 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   4,994
Fair Value | Level 2 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents 200,009 60,005
Fair Value | Level 3    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity investments in private companies 2,500  
Fair Value | Level 3 | Foreign exchange forward contracts    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset 0  
Derivative liability   0
Fair Value | Level 3 | U.S. term deposits    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 3 | U.S. federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 3 | Canadian federal bonds    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 3 | Corporate bonds and commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Marketable securities 0 0
Fair Value | Level 3 | Commercial paper    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents   0
Fair Value | Level 3 | Repurchase agreements    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and cash equivalents $ 0 $ 0