Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 165,081	$ 201,153
Prepaid expenses	13,148	4,152
Other current assets	326
Total current assets	178,555	205,305
Restricted cash	2,378
Property and equipment, net	8,386	265
Total assets	189,319	205,570
Current liabilities
Accounts payable	1,577	1,357
Accrued liabilities	12,821	12,899
Income taxes payable	247	247
Upfront payment from collaboration partner (Note 6)	40,000	40,000
Total current liabilities	54,645	54,503
Build-to-suit lease obligation	8,174
Total liabilities	62,819	54,503
Commitments and contingencies (Note 7)
Stockholders' equity
Common stock, $0.0001 par value, 50,000,000 shares authorized at March 31, 2017 and December 31, 2016; 35,162,043 and 34,843,885 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	3	3
Additional paid-in capital	445,565	440,667
Accumulated other comprehensive loss	(93)	(350)
Accumulated deficit	(318,975)	(289,253)
Total stockholders' equity	126,500	151,067
Total liabilities and stockholders’ equity	$ 189,319	$ 205,570