Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net (loss) income	$ (144,630)	$ 21,044
Adjustments to reconcile net (loss) income to cash flows from operating activities:
Gain from sale of Priority Review Voucher		(125,000)
Depreciation and amortization	5,125	3,409
Amortization of investment discount	(2,828)	(260)
Non-cash interest expense	9,958	117
Loss on disposal of assets	37	604
Stock-based compensation	25,805	16,177
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(13,517)	(12,563)
Net increase in inventory	(20,521)	(28,941)
Net increase in other assets	(29,866)	(9,285)
Net increase (decrease) in accounts payable, accrued expenses, deferred revenue and other liabilities	17,515	(8,337)
Net cash used in operating activities	(152,922)	(143,035)
Cash flows from investing activities:
Purchase of property and equipment	(20,863)	(7,336)
Purchase of intangible assets	(1,556)	(1,601)
Purchase of available-for-sale securities	(295,823)	(100,348)
Proceeds from sale of Priority Review Voucher		125,000
Purchases of restricted investment	(353)
Maturity of restricted investment		10,695
Maturity of available-for-sale securities	249,243	163,521
Net cash (used in) provided by investing activities	(69,352)	189,931
Cash flows from financing activities:
Proceeds from revolving line of credit	173,354
Payments on mortgage loans	(1,265)
Payments on revolving line of credit	(173,653)
Proceeds from exercise of options and purchase of stock under the Employee Stock Purchase Program	34,386	4,086
Repayments of long-term debt		(5,054)
Net cash provided by (used in) financing activities	32,822	(968)
(Decrease) increase in cash and cash equivalents	(189,452)	45,928
Cash, cash equivalents and restricted cash:
Beginning of period	599,827	122,556
End of period	410,375	168,484
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	410,375	168,348
Restricted cash in other assets		$ 136
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]		us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	410,375	$ 168,484
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	6,058	538
Supplemental schedule of non-cash investing activities and financing activities:
Shares withheld for taxes	5,750	309
Reclassification of long term investments to short term investments	9,980
Intangible assets included in accrued expenses	294	265
Asset held for sale		1,529
Accrual for debt issuance costs related to the term loans	600	$ 400
Property and equipment included in accrued expenses	$ 289