Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities
Net loss	$ (45,923)	$ (36,025)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	457	60
Amortization of deferred financing costs and debt discount	151	155
Amortization and accretion of premium or discount on available-for-sale investments, net	275	305
Stock-based compensation	7,415	6,217
Changes in operating assets and liabilities
Prepaid, current and other assets	791	(73)
Accounts payable and other current liabilities	(2,992)	(221)
Interest payable	(6)	(6)
Net cash used in operating activities	(39,832)	(29,588)
Cash flows from investing activities
Purchase of available-for-sale investments	(19,228)	(13,975)
Maturity of available-for-sale investments	24,815	24,088
Sale of available-for-sale investments	0	249
Purchase of furniture, fixtures and equipment	(459)	(1,052)
Net cash provided by investing activities	5,128	9,310
Cash flows from financing activities
Proceeds from sale of common stock, net of commissions	2,043	35,426
Proceeds from exercise of stock options	5	112
Proceeds from exercise of stock purchase rights	252	70
Tax withholdings related to restricted stock awards	(137)	0
Net cash provided by financing activities	2,163	35,608
Net change in cash and cash equivalents	(32,541)	15,330
Beginning of period	91,060	85,586
End of period	58,519	100,916
Supplemental disclosures
Income taxes paid	1,789	469
Interest paid	$ 1,096	$ 1,090