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Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Oct. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	7,258,353	6,706,994
Weighted average exercise price (in dollars per share)	$ 21.48	$ 22.33
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 20,676	$ 19,571	$ 16,520
Equity Incentive Plan 2003
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	249,959
Weighted average exercise price (in dollars per share)	$ 2.79
Stock Incentive Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized (in shares)				1,960,168
Increased number of shares authorized (in shares)	11,896,613
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	7,008,394
Weighted average exercise price (in dollars per share)	$ 22.14
Minimum annual increase (in shares)	1,960,168
Percentage of common stock share outstanding	4.00%
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 10,833	10,023	7,919
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9,843	$ 9,548	$ 8,601

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