Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 11,628	$ 10,258
Short-term investments	120,945	123,055
Accounts receivable from related party	4	393
Prepaid expenses and other current assets	1,110	596
Total current assets	133,687	134,302
Property and equipment, net	1,278	1,399
Long-term investments	9,336	16,561
Other assets	160	160
Total assets	144,461	152,422
Current liabilities:
Accounts payable	710	909
Accrued liabilities	6,187	5,649
Current portion of equipment financing obligations	184	314
Total current liabilities	7,081	6,872
Noncurrent equipment financing obligations		16
Other non-current liabilities	195	226
Total liabilities	7,276	7,114
Preferred stock:
Preferred stock, $0.001 par value, 10,000,000 shares authorized; no shares issued and outstanding;
Common stock, $0.001 par value, 200,000,000 shares authorized at March 31, 2014 and December 31, 2013; 43,172,171 shares and 42,888,168 shares issued and outstanding at March 31, 2014 and December 31, 2013, respectively.	43	43
Additional paid-in capital	321,499	318,103
Note receivable	(16)	(16)
Accumulated other comprehensive income	58	40
Accumulated deficit	(184,399)	(172,862)
Total stockholders' equity	137,185	145,308
Total liabilities and stockholders' equity	$ 144,461	$ 152,422