Income Taxes - Variation Between Expected and Effective Tax Rate (Details)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%	21.00%
State income taxes (net of federal benefit)	4.60%	3.60%	5.30%
Foreign derived intangible income deduction	(0.004)	(0.012)	0
Stock-based compensation expense	(1.40%)	(2.10%)	(1.90%)
Research and development tax credits	(13.80%)	(7.80%)	(32.00%)
Other tax credits	(0.30%)	0.00%	(1.20%)
Changes in valuation allowance	(0.40%)	(1.60%)	0.70%
Non-deductible book expenses	3.60%	3.90%	8.20%
Changes in deferred tax assets	(0.20%)	(2.20%)	12.10%
Changes in tax reserves	(4.60%)	1.20%	1.20%
Other	0.70%	(0.80%)	(1.40%)
Effective income tax rate	8.80%	14.00%	12.00%
Tax credit, percent	(3.40%)

Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets, Percent

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Effective Income Tax Rate Reconciliation Tax Reserves

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 12
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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 740
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to changes in the valuation allowance for deferred tax assets.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-SubTopic 10
-Section S99
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Percentage of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to nondeductible expense for share-based payment arrangement.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations applicable to state and local income tax expense (benefit), net of federal tax expense (benefit).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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Percentage of reported income tax expense (benefit) in excess of (less than) expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operations, attributable to increase (decrease) from transition tax on accumulated earnings of controlled foreign corporation deemed repatriated pursuant to Tax Cuts and Jobs Act.

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