Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities
Net loss	$ (36,025)	$ (18,485)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	60	31
Amortization of deferred financing costs and debt discount	155	0
Amortization of discount on available-for-sale investments	305	157
Stock-based compensation	6,217	4,304
Changes in operating assets and liabilities
Prepaid, current and other assets	(73)	(292)
Accounts payable and other current liabilities	(221)	1,364
Interest payable	(6)	0
Net cash used in operating activities	(29,588)	(12,921)
Cash flows from investing activities
Purchase of available-for-sale investments	(13,975)	(31,852)
Maturity of available-for-sale investments	24,088	2,985
Sale of available-for-sale investments	249	0
Purchase of furniture, fixtures and equipment	(1,052)	(59)
Net cash provided by (used in) investing activities	9,310	(28,926)
Cash flows from financing activities
Proceeds from sale of common stock	35,426	0
Proceeds from exercise of stock options	112	9
Proceeds from exercise of stock purchase rights	70	65
Net cash provided by financing activities	35,608	74
Net change in cash and cash equivalents	15,330	(41,773)
Beginning of period	85,586	69,649
End of period	100,916	27,876
Supplemental disclosures
Interest paid	1,090	0
Income taxes paid	$ 469	$ 0