Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 63,001	$ 117,773
Short-term investments	198,433	150,892
Receivables from collaborations	6,664	309
Prepaid expenses and other current assets	5,168	3,733
Total current assets	273,266	272,707
Property and equipment, net	2,670	2,600
Long-term investments	44,269	50,371
Other assets	34	53
Total assets	320,239	325,731
Current liabilities:
Accounts payable	7,380	3,232
Accrued compensation and employee benefits	1,649	2,569
Accrued and other liabilities	14,990	17,796
Deferred revenue, current portion	8,779	1,958
Total current liabilities	32,798	25,555
Deferred revenue, long-term	17,060	3,253
Other long-term liabilities	1,189	588
Total liabilities	51,047	29,396
Stockholders’ equity:
Preferred stock, $0.001 par value, 5,000,000 shares authorized at March 31, 2014 and December 31, 2013; 0 shares issued and outstanding at March 31, 2014 and December 31, 2013
Common stock, $0.001 par value, 100,000,000 shares authorized at March 31, 2014 and December 31, 2013; 41,120,789 and 40,915,130 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively	41	41
Additional paid-in capital	585,522	581,911
Accumulated deficit	(316,398)	(285,672)
Accumulated other comprehensive income	27	55
Total stockholders’ equity	269,192	296,335
Total liabilities and stockholders’ equity	$ 320,239	$ 325,731