Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities
Net loss	$ (22,704)	$ (17,239)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	223	24
Amortization of deferred financing costs and debt discount	75	77
Amortization of discount on available-for-sale investments	147	163
Stock-based compensation	3,534	2,741
Changes in operating assets and liabilities
Prepaid, current and other assets	503	(205)
Accounts payable and other current liabilities	(1,130)	1,144
Interest payable	(6)	(12)
Net cash used in operating activities	(19,358)	(13,307)
Cash flows from investing activities
Purchase of available-for-sale investments	(13,265)	(8,188)
Maturity of available-for-sale investments	16,036	14,828
Purchase of furniture, fixtures and equipment	(335)	(539)
Net cash provided by investing activities	2,436	6,101
Cash flows from financing activities
Proceeds from sale of common stock, net of commissions	0	35,000
Proceeds from exercise of stock options	4	0
Proceeds from exercise of stock purchase rights	252	70
Tax withholdings related to restricted stock awards	(128)	0
Net cash provided by financing activities	128	35,070
Net change in cash and cash equivalents	(16,794)	27,864
Beginning of period	91,060	85,586
End of period	74,266	113,450
Supplemental disclosures
Income taxes paid	1,789	0
Interest paid	$ 551	$ 551