Condensed Consolidated Statements of Cash Flows $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Cash flows from operating activities:
Net loss	$ (221,023)	$ (26,690)
Adjustments to reconcile net loss to cash flows from operating activities:
Gain from sale of Priority Review Voucher		(125,000)
Depreciation and amortization	8,718	5,968
Amortization of investment discount	(4,742)	(344)
Loss from debt extinguishment	2,322
Non-cash interest expense	15,206	200
Loss on disposal of assets	94	792
Stock-based compensation	37,289	23,099
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(19,133)	(19,523)
Net increase in inventory	(32,211)	(51,880)
Net increase in other assets	(84,344)	(7,319)
Net increase (decrease) in accounts payable, accrued expenses, deferred revenue and other liabilities	31,584	(241)
Net cash used in operating activities	(266,240)	(200,938)
Cash flows from investing activities:
Purchase of property and equipment	(40,954)	(8,101)
Purchase of intangible assets	(2,633)	(8,591)
Purchase of available-for-sale securities	(651,387)	(100,348)
Maturity and sale of available-for-sale securities	562,575	296,225
Proceeds from sale of Priority Review Voucher		125,000
Purchases of restricted investment	(353)
Maturity of restricted investment		10,695
Net cash (used in) provided by investing activities	(132,752)	314,880
Cash flows from financing activities:
Proceeds from July 2017 Term Loan, net of cash debt issuance costs		29,620
Repayment of June 2015 and July 2017 Term Loan	(30,000)	(15,000)
Proceeds from revolving line of credit	217,722	24,000
Repayment of revolving line of credit	(218,631)	(23,008)
Repayments on mortgage loans	(1,265)	(81)
Payment of debt extinguishment	(1,990)
Proceeds from sale of common stock, net of offering costs		353,959
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	43,031	11,779
Net cash provided by financing activities	8,867	381,269
(Decrease) increase in cash and cash equivalents	(390,125)	495,211
Cash, cash equivalents and restricted cash:
Beginning of period	599,827	122,556
End of period	209,702	617,767
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	209,702	617,630
Restricted cash in other assets		$ 137
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	209,702	$ 617,767
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	6,861	924
Supplemental schedule of non-cash investing activities and financing activities:
Shares withheld for taxes	9,053	1,791
Reclassification of long term investments to short term investments	9,980
Reclassification of revolving line of credit balance to other receivable	683
Intangible assets included in accrued expenses	234	258
Asset held for sale		1,529
Debt issuance costs related to the term loans included in accrued expenses		600
Offering costs related to equity offerings included in accrued expenses		25
Property and equipment included in accrued expenses	$ 2,515	$ 385