Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities
Net loss	$ (53,986)	$ (31,632)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	102	50
Amortization of deferred financing costs and debt discount	232	0
Amortization of discount on available-for-sale investments	439	247
Stock-based compensation	9,533	6,696
Changes in operating assets and liabilities
Prepaid, current and other assets	(238)	(20)
Accounts payable and other current liabilities	2,407	2,267
Net cash used in operating activities	(41,511)	(22,392)
Cash flows from investing activities
Purchase of available-for-sale investments	(26,560)	(34,593)
Maturity of available-for-sale investments	40,813	10,660
Sale of available-for-sale investments	1,999	1,500
Purchase of furniture, fixtures and equipment	(1,855)	(146)
Net cash provided by (used in) investing activities	14,397	(22,579)
Cash flows from financing activities
Proceeds from sale of common stock	47,100	0
Proceeds from exercise of stock options	1,269	9
Proceeds from exercise of warrants	9	0
Proceeds from exercise of stock purchase rights	96	119
Proceeds from issuance of convertible notes, net of discounts	0	124,375
Payments of debt issuance costs	0	(297)
Net cash provided by financing activities	48,474	124,206
Net change in cash and cash equivalents	21,360	79,235
Beginning of period	85,586	69,649
End of period	106,946	148,884
Supplemental disclosures
Interest paid	1,635	0
Income taxes paid	600	0
Noncash financing activities
Debt Issuance Costs Incurred During Noncash or Partial Noncash Transaction	0	250
Deferred financing costs	$ 0	$ 1,000