Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (42,296)	$ (35,522)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	928	798
Loss from valuation of convertible note payable	0	1,811
Stock-based compensation	5,986	8,972
Amortization of premium on investments, net	359	801
Other	45	56
Change in operating assets and liabilities:
Contracts and other receivables	9,878	(50)
Prepaid expenses	594	826
Other assets	270	20
Accounts payable	787	130
Accrued liabilities	(1,063)	2,459
Accrued compensation	(529)	167
Deferred revenue	(972)	(1,323)
Deferred rent and other liabilities	(262)	(160)
Net cash used in operating activities	(26,275)	(21,015)
Investing activities
Purchases of short-term investments	(30,231)	(46,281)
Sales and maturities of short-term investments	47,522	49,645
Purchases of property and equipment	(266)	(410)
Acquisition of intangibles	(34)	(19)
Net cash provided by investing activities	16,991	2,935
Financing activities
Proceeds from borrowing under term loan, net	19,819	0
Proceeds from issuance of common stock, net	363	257
Proceeds from exercise of common stock options	265	1,655
Principal payments on other long-term obligations	(83)	(75)
Net cash provided by financing activities	20,364	1,837
Net increase (decrease) in cash and cash equivalents	11,080	(16,243)
Cash and cash equivalents at beginning of period	15,960	37,327
Cash and cash equivalents at end of period	27,040	21,084
Supplemental disclosure of cash flow information
Net changes in restricted cash	(794)	0
Interest paid	(54)	(15)
Income taxes paid	(1)	(1)
Supplemental disclosure of non-cash investing and financing activities
Allowance for tenant improvements	6,545	0
Amounts accrued for property and equipment	221	90
Amounts accrued for patent expenditures	7	0
Unpaid debt issuance costs	$ 38	$ 0