Income Taxes - Significant Components of Net Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating losses	$ 47,218	$ 26,676
Tax credits	4,937	2,473
Accruals	1,174	1,117
Share-based compensation	8,966	3,769
Gross deferred tax assets	62,295	34,035
Valuation allowance	(56,382)	(31,185)
Net deferred tax assets	5,913	2,850
Deferred tax liability	0	0
Net deferred tax assets	$ 5,913	$ 2,850