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Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	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)	6,706,994	5,273,964
Weighted average exercise price (in dollars per share)	$ 22.33	$ 22.23
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 19,571	$ 16,520	$ 14,744
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)	550,572
Weighted average exercise price (in dollars per share)	$ 2.32
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)	9,932,263
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	6,156,422
Weighted average exercise price (in dollars per share)	$ 24.12
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	$ 10,023	7,919	7,388
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9,548	$ 8,601	$ 7,356

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