Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Cash Flows [Abstract]
Net loss	$ (21,149)	$ (13,354)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	729	285
Amortization of intangible assets	5	38
Amortization on investment instruments	99	124
Equity-based compensation	4,185	4,931
(Increase) decrease in assets:
Accounts receivable	(65)	(16)
Prepaid expense and other	(675)	(486)
Increase (decrease) in liabilities:
Accounts payable	(129)	496
Accrued liabilities	657	197
Deferred income	(14)	(20)
Net cash used in operating activities	(16,357)	(7,805)
Purchases of equipment	(2,160)	(729)
Purchase of available-for-sale securities	(8,017)	(4,079)
Sales of available-for-sale securities	141	121
Maturity of available-for-sale securities	7,807	2,000
Net cash used in investing activities	$ (2,229)	(2,687)
Issuance of common stock		44,980
Exercise of options	$ 327	730
Payments on capital lease obligations	(73)	(35)
Net cash provided by financing activities	254	45,675
(Decrease) increase in cash and cash equivalents	(18,332)	35,183
Cash and cash equivalents, beginning of period	53,563	30,029
Cash and cash equivalents, end of period	$ 35,231	$ 65,212