Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss		$ (267,265)	$ (220,030)	$ (135,789)
Adjustments to reconcile net income to cash flows in operating activities:
Depreciation and amortization		5,611	5,247	3,690
Amortization of premium, net of discount, on available-for-sale securities and loss from sales of available-for-sale securities		80	652	2,432
Non-cash interest expense		355	367	12
Loss on abandonment of patents		293	197	128
Stock-based compensation		29,962	32,117	20,345
Non-cash restructuring expense	[1]	911
Increase in warrant valuation		0	0	2,779
Changes in operating assets and liabilities, net:
(Increase) decrease in accounts receivable		(1,251)	(1,561)	1,114
Increase in inventory		(12,813)
(Increase) decrease in other assets		(9,012)	15,249	(34,013)
Increase in accounts payable, accrued expenses, deferred revenue and other liabilities		7,309	18,297	10,763
Net cash used in operations		(245,820)	(149,465)	(128,539)
Cash flows from investing activities:
Release and maturity of restricted investments				7,250
Purchase of restricted investment			(10,695)
Purchase of property and equipment		(5,341)	(3,401)	(25,444)
Patent costs		(1,525)	(1,432)	(1,381)
Purchase of available-for-sale securities		(195,427)	(162,001)	(274,368)
Maturity and sales of available-for-sale securities		112,100	185,939	134,913
Net cash (used in) provided by investing activities		(90,193)	8,410	(159,030)
Cash flows from financing activities:
Proceeds from borrowings, net of debt issuance costs			19,601
Repayments of long-term debt and notes payable		(7,603)	(2,598)	(94)
Proceeds from sales of common stock, net of offering costs		364,802	119,916	94,503
Proceeds from exercise of options and warrants and employee stock purchase program		20,930	10,889	9,746
Net cash provided by financing activities		378,129	147,808	104,155
Increase (decrease) in cash and cash equivalents		42,116	6,753	(183,414)
Cash and cash equivalents:
Beginning of period		80,304	73,551	256,965
End of period		122,420	80,304	73,551
Supplemental disclosure of cash flow information:
Cash paid during the period for interest		1,562	769	77
Supplemental schedule of non-cash investing activities and financing activities:
Accrued debt issuance costs related to the senior secured term loan		400	400
Property and equipment included in accrued expenses		1,186	318	277
Intangible assets included in accrued expenses		1,163	335	270
Issuance of common stock in satisfaction of warrants				11,785
Shares withheld for taxes		2,168	$ 182	34
Issuance of notes payable in relation to the purchase of certain real and personal property located in Andover, Massachusetts				$ 4,613
Accrual for offering costs related to the equity offerings		$ 53

[1] The non-cash restructuring expenses include the following: $0.8 million accelerated depreciation for certain assets $0.1 million acceleration of stock option vesting