Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (157,803)	$ (100,048)	$ (46,514)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization of fixed assets	7,600	3,710	1,418
Loss on disposal of property and equipment	40	49	100
Stock-based compensation	18,050	11,520	7,744
Amortization of deferred license fees		(294)	(4,144)
Amortization of other liabilities	(573)
Amortization of deferred financing costs	44
Forgiveness of long-term debt	(1,000)
Amortization of premium on short-term investments	1,323	842	636
Amortization of intangible assets	150
Changes in assets and liabilities:
Accounts receivable	(3,557)	(1,376)
Inventory, net	(2,660)	(4,017)
Prepaid expenses and other current assets	(3,057)	(1,329)	(1,606)
Accounts payable	661	1,886	(2,891)
Accrued liabilities	7,424	8,064	2,299
Lease incentive obligation	(553)	(487)	2,655
Accrued interest	(106)	22	21
Net cash used in operating activities	(134,017)	(81,458)	(40,282)
Cash flows from investing activities:
Purchases of marketable securities	(205,054)	(209,471)	(98,510)
Maturities of marketable securities	162,283	104,172	72,289
Purchases of property and equipment	(20,084)	(11,991)	(8,748)
Purchases of intangible assets	(1,900)
Net cash used in investing activities	(64,755)	(117,290)	(34,969)
Cash flows from financing activities:
Proceeds from exercise of common stock options	1,248	2,640	1,341
Proceeds from sale of common stock, net of issuance costs	174,140	238,580	73,296
Payments on capital lease obligations	(360)	(351)	(333)
Payments on mortgage payable	(44)
Proceeds from mortgage payable	5,062
Proceeds from New Market Tax Credit financing agreements		2,399
Proceeds in connection with the Company's employee stock purchase plan	1,719	760	453
Net cash provided by financing activities	181,765	244,028	74,757
Effects of exchange rate on cash and cash equivalents	11
Net (decrease) increase in cash and cash equivalents	(16,996)	45,280	(494)
Cash and cash equivalents, beginning of period	58,131	12,851	13,345
Cash and cash equivalents, end of period	41,135	58,131	12,851
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment acquired but not paid	1,705	546	534
Unrealized gain on available-for-sale investments	(329)	(240)	47
Issuance of 21,826 and 32,669 shares of common stock to fund the Company’s 401(k) matching contribution for 2015 and 2014, respectively	836	456	354
Interest paid	$ 95	$ 29	$ 48