Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Statement of Cash Flows [Abstract]
Net loss	$ (32,335)	$ (22,168)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,194	536
Amortization of intangible assets	8	56
Amortization on investment instruments	147	229
Equity-based compensation	5,995	7,334
Increase in assets:
Accounts receivable	(664)	(65)
Prepaid expense and other	(642)	(547)
(Decrease) increase in liabilities:
Accounts payable	(329)	528
Accrued liabilities	1,400	125
Deferred income	(14)	(22)
Net cash used in operating activities	(25,240)	(13,994)
Purchases of equipment	(2,594)	(1,357)
Purchase of available-for-sale securities	(12,418)	(6,614)
Sales of available-for-sale securities	141	246
Maturity of available-for-sale securities	11,307	4,007
Net cash used in investing activities	$ (3,564)	(3,718)
Issuance of common stock		44,875
Exercise of options	$ 542	730
Payments on capital lease obligations	(110)	(71)
Net cash provided by financing activities	432	45,534
(Decrease) increase in cash and cash equivalents	(28,372)	27,822
Cash and cash equivalents, beginning of period	53,563	30,029
Cash and cash equivalents, end of period	$ 25,191	$ 57,851