Stock- based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended			84 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2012	Oct. 31, 2013	Feb. 28, 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)	3,838,060	4,146,064
Weighted average exercise price (in dollars per share)	$ 18.93	$ 16.90
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 12,165	$ 7,847	$ 3,244
Equity Incentive Plan 2003
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, number of shares authorized (in shares)						2,051,644
Increased number of shares authorized (in shares)				4,336,730
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	1,193,941
Weighted average exercise price (in dollars per share)	$ 1.81
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)	5,375,064
Share-based compensation arrangement by share-based payment award, options, outstanding, number (in shares)	2,644,119
Weighted average exercise price (in dollars per share)	$ 26.66
Stock reserved for future issuance (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	$ 5,778	3,623	1,562
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 6,387	$ 4,224	$ 1,682