Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 77,722	$ 57,514
Short-term investments	278,246	251,759
Receivables from collaborators		57
Prepaid expenses and other current assets	20,499	5,747
Total current assets	376,467	315,077
Property and equipment, net	5,406	2,776
Long-term investments		83,030
Prepaid and other long-term assets	12,987	15,612
Total assets	394,860	416,495
Current liabilities:
Accounts payable	9,173	14,084
Accrued compensation and employee benefits	3,841	3,512
Accrued research and development	23,742	12,545
Accrued and other liabilities	3,697	1,421
Deferred revenue, current portion	8,705	9,569
Total current liabilities	49,158	41,131
Deferred revenue, long-term	20,726	27,016
Other long-term liabilities	2,068	546
Total liabilities	$ 71,952	$ 68,693
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value, 100,000,000 shares authorized at September 30, 2015 and December 31, 2014; 52,704,383 and 48,766,806 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	$ 53	$ 49
Additional paid-in capital	906,031	770,789
Accumulated deficit	(583,196)	(422,797)
Accumulated other comprehensive income/(loss)	20	(239)
Total stockholders’ equity	322,908	347,802
Total liabilities and stockholders’ equity	$ 394,860	$ 416,495