Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 143,358	$ 201,153
Prepaid expenses	11,297	4,152
Other current assets	326
Total current assets	154,981	205,305
Restricted cash	2,378
Property and equipment, net	590	265
Build-to-suit lease asset	9,975
Total assets	167,924	205,570
Current liabilities
Accounts payable	2,550	1,357
Accrued liabilities	22,181	12,899
Income taxes payable		247
Upfront payment from collaboration partner (Note 5)	40,000	40,000
Total current liabilities	64,731	54,503
Build-to-suit lease obligation	8,174
Total liabilities	72,905	54,503
Commitments and contingencies (Note 6)
Stockholders' equity
Common stock, $0.0001 par value, 50,000,000 shares authorized at June 30, 2017 and December 31, 2016; 35,514,630 and 34,843,885 shares issued and outstanding at June 30, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	450,588	440,667
Accumulated other comprehensive loss	0	(350)
Accumulated deficit	(355,572)	(289,253)
Total stockholders' equity	95,019	151,067
Total liabilities and stockholders’ equity	$ 167,924	$ 205,570