Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 81,146	$ 201,153
Prepaid expenses and other current assets	562	4,152
Total current assets	81,708	205,305
Restricted cash	2,383
Property and equipment, net	798	265
Build-to-suit lease asset	8,888
Total assets	93,777	205,570
Current liabilities
Accounts payable	1,500	1,357
Accrued liabilities	4,093	12,899
Income taxes payable		247
Upfront payment from collaboration partner (Note 6)		40,000
Total current liabilities	5,593	54,503
Build-to-suit lease obligation (Note 7)	5,428
Total liabilities	11,021	54,503
Commitments and contingencies (Note 8)
Stockholders' equity
Preferred stock, $0.0001 par value, 5,000,000 shares authorized at December 31, 2017 and December 31, 2016; zero shares issued and outstanding at December 31, 2017 and December 31, 2016
Common stock, $0.0001 par value, 100,000,000 and 50,000,000 shares authorized at December 31, 2017 and December 31, 2016, respectively; 35,938,126 and 34,843,885 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	4	3
Additional paid-in capital	456,984	440,667
Accumulated other comprehensive loss		(350)
Accumulated deficit	(374,232)	(289,253)
Total stockholders' equity	82,756	151,067
Total liabilities and stockholders’ equity	$ 93,777	$ 205,570