CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (550,056)	$ (348,647)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation, amortization and accretion, net	8,663	9,653
Stock-based compensation	129,779	65,702
Non-cash gain on litigation settlement	(10,000)
Charge for 401(k) company stock match	3,612	1,735
Unrealized gain on marketable equity securities	(5,004)
Realized loss on sale of marketable equity securities		1,894
Other		608
Changes in operating assets and liabilities:
Proceeds from landlord lease incentive for tenant improvements	11,597
Accounts receivable, net	(30,640)	(8,690)
Inventory	(10,354)
Prepaid expenses and other assets	(34,125)	(2,052)
Accounts payable	(650)	(17,271)
Accrued expenses and other	25,242	5,990
Deferred revenue	(11,503)	(6,044)
Net cash used in operating activities	(412,159)	(279,742)
Cash flows from investing activities:
Purchases of property, plant and equipment	(89,374)	(83,481)
Purchases of restricted investments	(14,825)
Purchases of marketable debt securities	(992,385)	(512,026)
Sales and maturities of marketable securities	1,120,565	465,734
Net cash provided by (used in) investing activities	23,981	(129,773)
Cash flows from financing activities:
Proceeds from exercise of stock options and other types of equity	61,268	41,600
Proceeds from issuance of common stock, net of offering costs		355,150
Proceeds from issuance of common stock to Sanofi Genzyme		21,381
Payments for repurchase of common stock for employee tax withholding	(1,176)	(188)
Net cash provided by financing activities	60,092	417,943
Net (decrease) increase in cash, cash equivalents and restricted cash	(328,086)	8,428
Cash, cash equivalents and restricted cash, beginning of period	646,832	195,088
Cash, cash equivalents and restricted cash, end of period	$ 318,746	$ 203,516