Short-term Investments - Assets Classified on Consolidated Balance Sheets (Details) - USD ($) $ in Thousands |
Jun. 30, 2015 |
Dec. 31, 2014 |
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|---|---|---|---|---|
| Schedule of Available-for-sale Securities [Line Items] | ||||
| Total | $ 2,801,692 | $ 1,614,190 | ||
| Fair Value, Measurements, Recurring [Member] | ||||
| Schedule of Available-for-sale Securities [Line Items] | ||||
| Total | 2,801,692 | 1,614,190 | ||
| Cash and cash equivalents [Member] | Fair Value, Measurements, Recurring [Member] | ||||
| Schedule of Available-for-sale Securities [Line Items] | ||||
| Total | 2,293,872 | 1,113,608 | ||
| Short-term investments [Member] | Fair Value, Measurements, Recurring [Member] | ||||
| Schedule of Available-for-sale Securities [Line Items] | ||||
| Total | 502,886 | 494,888 | ||
| Other non-current assets [Member] | Fair Value, Measurements, Recurring [Member] | ||||
| Schedule of Available-for-sale Securities [Line Items] | ||||
| Total | [1] | $ 4,934 | $ 5,694 | |
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