Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (21,207)	$ (14,487)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	419	394
Loss from valuation of convertible note payable	0	1,811
Stock-based compensation	3,749	3,103
Amortization of premium on investments, net	198	425
Loss on disposal of long-term assets	0	50
Change in operating assets and liabilities:
Contracts and other receivables	9,959	(2,469)
Prepaid expenses	(1,113)	(148)
Other assets	338	226
Accounts payable	906	471
Accrued liabilities	(596)	899
Accrued compensation	(1,181)	(1,059)
Deferred revenue	(489)	(389)
Deferred rent and other liabilities	87	(79)
Net cash used in operating activities	(8,930)	(11,252)
Investing activities
Purchases of short-term investments	(20,475)	(37,157)
Sales and maturities of short-term investments	32,572	30,010
Purchases of property and equipment	(395)	(236)
Acquisition of intangibles	(11)	(7)
Net cash provided by (used in) investing activities	11,691	(7,390)
Financing activities
Proceeds from issuance of common stock, net	363	257
Proceeds from exercise of common stock options	206	695
Principal payments on other long-term obligations	(41)	(37)
Net cash provided by financing activities	528	915
Net increase (decrease) in cash and cash equivalents	3,289	(17,727)
Cash and cash equivalents at beginning of period	15,960	37,327
Cash and cash equivalents at end of period	19,249	19,600
Supplemental disclosure of cash flow information
Net changes in restricted cash	(338)	0
Interest paid	(5)	(8)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Allowance for tenant improvements	5,470	0
Amounts accrued for property and equipment	$ 86	$ 14