Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 68,911	$ 57,514
Short-term investments	332,596	251,759
Receivables from collaborators		57
Prepaid expenses and other current assets	15,967	5,747
Total current assets	417,474	315,077
Property and equipment, net	4,584	2,776
Long-term investments	6,091	83,030
Prepaid and other long-term assets	13,910	15,612
Total assets	442,059	416,495
Current liabilities:
Accounts payable	12,625	14,084
Accrued compensation and employee benefits	2,989	3,512
Accrued and other liabilities	24,492	13,966
Deferred revenue, current portion	9,021	9,569
Total current liabilities	49,127	41,131
Deferred revenue, long-term	22,820	27,016
Other long-term liabilities	2,079	546
Total liabilities	$ 74,026	$ 68,693
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized at June 30, 2015 and December 31, 2014; no shares issued and outstanding at June 30, 2015 and December 31, 2014
Common stock, $0.001 par value, 100,000,000 shares authorized at June 30, 2015 and December 31, 2014; 52,394,531 and 48,766,806 shares issued and outstanding at June 30, 2015 and December 31, 2014, respectively	$ 52	$ 49
Additional paid-in capital	896,110	770,789
Accumulated deficit	(528,038)	(422,797)
Accumulated other comprehensive loss	(91)	(239)
Total stockholders’ equity	368,033	347,802
Total liabilities and stockholders’ equity	$ 442,059	$ 416,495