Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash flows from operating activities:
Net loss	$ (92,238)	$ (74,867)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization of fixed assets	5,289	3,377
Loss on disposal of property and equipment	44
Stock-based compensation	10,607	8,168
Amortization of other liabilities	(445)	(241)
Amortization of deferred financing costs	26
Forgiveness of long-term debt		(1,000)
Amortization of premium on short-term investments	346	702
Amortization of intangible assets	100
Changes in assets and liabilities:
Accounts receivable, net	(2,508)	(775)
Inventory, net	(1,727)	(2,258)
Prepaid expenses and other current assets	80	(291)
Accounts payable	(173)	(1,302)
Accrued liabilities	2,651	2,212
Lease incentive obligation	(23)	(276)
Accrued interest		(106)
Net cash used in operating activities	(77,971)	(66,657)
Cash flows from investing activities:
Purchases of marketable securities	(6,118)	(19,318)
Maturities of marketable securities	97,004	66,324
Purchases of property and equipment	(6,415)	(9,773)
Net cash used in investing activities	84,471	37,233
Cash flows from financing activities:
Proceeds from exercise of common stock options	549	859
Payments on capital lease obligations		(183)
Proceeds from mortgage payable		3,656
Payments on mortgage payable	(82)
Proceeds in connection with the Company's employee stock purchase plan	1,047	758
Net cash provided by financing activities	1,514	5,090
Effects of exchange rate on cash and cash equivalents	(139)	(32)
Net increase (decrease) in cash and cash equivalents	7,875	(24,366)
Cash and cash equivalents, beginning of period	41,135	58,131
Cash and cash equivalents, end of period	49,010	33,765
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment acquired but not paid	1,055	969
Unrealized gain on available-for-sale investments	555	136
Issuance of 340,950 and 21,826 shares of common stock to fund the Company's 401(k) matching contribution for 2015 and 2014, respectively	2,151	835
Interest paid	$ 105	$ 8