Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (25,226)	$ (24,084)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation of property and equipment	173	259
Stock-based compensation	4,641	4,752
Noncash interest expense, net	(124)	625
Changes in assets and liabilities:
Accounts receivable	(175)
Prepaids and other current assets	(400)	72
Other assets	(70)
Accounts payable	(162)	280
Deferred revenue	75,380
Other liabilities	1,878	(3,241)
Net cash provided by (used in) operating activities	55,915	(21,337)
Investing activities
Purchases of property and equipment, net	(82)	(118)
Purchases of investments	(95,907)	(18,351)
Maturities of investments	41,688	29,700
Sales of investments	0	4,051
Net cash provided by (used in) investing activities	(54,301)	15,282
Financing activities
Proceeds from issuance of common stock	7,000
Proceeds from exercise of stock options and employee stock purchase plan	488	1,550
Net cash provided by financing activities	7,488	1,550
Net increase (decrease) in cash and cash equivalents	9,102	(4,505)
Cash and cash equivalents at beginning of period	12,823	16,075
Cash and cash equivalents at end of period	$ 21,925	$ 11,570