Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 170,262	$ 31,014
Short-term investments, available for sale	199,745	162,795
Receivables under collaboration agreements	30,030
Other current assets	4,916	4,394
Total current assets	404,953	198,203
Property and equipment, net	2,543	2,507
Long-term investments, available for sale	115,452	37,492
Restricted cash	4,831	4,831
Total assets	527,779	243,033
Current liabilities:
Accounts payable	1,270	246
Accrued liabilities	9,938	11,508
Current portion of cease-use liability	479	467
Current portion of deferred rent	152	119
Current portion of deferred gain on sale of real estate	3,348	3,324
Total current liabilities	15,187	15,664
Deferred gain on sale of real estate	13,468	14,322
Deferred revenue	10,231	0
Deferred rent	1,817	1,877
Cease-use liability	2,086	2,211
Other liabilities	260	260
Total liabilities	43,049	34,334
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.001 par value; 110,000,000 shares authorized; issued and outstanding shares were 85,372,303 as of March 31, 2015 and 76,465,942 as of December 31, 2014	85	76
Additional paid-in capital	1,312,321	1,035,205
Accumulated other comprehensive loss	(179)	(277)
Accumulated deficit	(827,497)	(826,305)
Total stockholders' equity	484,730	208,699
Total liabilities and stockholders' equity	$ 527,779	$ 243,033