Global intangible low taxed income provision amount.

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Income taxes disclosure.

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Net operating loss carryforwards, expiration beginning year.

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Tax credit carryforwards expiration beginning year.

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Tax cut and jobs act of 2017 compensation deduction highest paid officers threshold limit.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

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Amount of unrecognized tax benefits.

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Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

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Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes Disclosure [Line Items]
Research and development tax credit carryforwards	$ 39,344,000	$ 15,475,000
Unrecognized tax benefits	14,541,000	$ 5,843,000	$ 4,368,000
Accrued interest and penalties	0
Unrecognized tax benefits that would impact effective tax rate	$ 0
US federal corporate tax rate	21.00%	34.00%	34.00%
Maximum
Income Taxes Disclosure [Line Items]
Average annual gross receipts	$ 500,000,000
Tax cut and jobs act of 2017 Compensation Deduction highest paid officers threshold limit	1,000,000
Research and Development Credits
Income Taxes Disclosure [Line Items]
Unrecognized tax benefits	14,500,000
Federal
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	$ 495,900,000
Net operating loss carryforwards, expiration beginning year	2028
Research and development tax credit carryforwards	$ 33,900,000
Tax credit carryforwards, expiration beginning year	2028
US federal corporate tax rate	21.00%	35.00%
State
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	$ 408,300,000
Net operating loss carryforwards, expiration beginning year	2028
Research and development tax credit carryforwards	$ 23,200,000
UK
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	3,000,000
Research and development tax credit carryforwards	$ 100,000