Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (479,372)	$ (221,023)
Adjustments to reconcile net loss to cash flows from operating activities:
Acquired in-process research and development	173,240
Depreciation and amortization	22,341	8,718
Amortization of investment discount	(7,449)	(4,742)
Loss from debt extinguishment		2,322
Non-cash interest expense	15,887	15,206
Stock-based compensation	56,538	37,289
Other	892	94
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(18,988)	(19,133)
Net increase in inventory	(40,915)	(32,211)
Net increase in other assets	(94,710)	(84,344)
Net increase in accounts payable, accrued expenses, deferred revenue and other liabilities	79,868	31,584
Net cash used in operating activities	(292,668)	(266,240)
Cash flows from investing activities:
Purchase of property and equipment	(42,374)	(40,954)
Purchase of intangible assets	(2,048)	(2,633)
Purchase of available-for-sale securities	(984,225)	(651,387)
Purchases of restricted investment		(353)
Maturity and sale of available-for-sale securities	1,470,848	562,575
Net cash provided by (used in) investing activities	269,645	(132,752)
Cash flows from financing activities:
Proceeds from sale of common stock, net of offering costs	365,353
Taxes paid related to net share settlement of equity awards	(4,337)
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	24,572	43,031
Repayment of June 2015 and July 2017 Term Loan		(30,000)
Proceeds from revolving line of credit		217,722
Repayment of revolving line of credit		(218,631)
Repayments on mortgage loans		(1,265)
Payment of debt extinguishment		(1,990)
Net cash provided by financing activities	385,588	8,867
Increase (decrease) in cash, cash equivalents and restricted cash	362,565	(390,125)
Cash, cash equivalents and restricted cash:
Beginning of period	370,829	599,827
End of period	733,394	209,702
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	724,829	$ 209,702
Restricted cash in other assets	$ 8,565
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 733,394	$ 209,702
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	4,275	6,861
Supplemental schedule of non-cash investing activities and financing activities:
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	210	234
Property and equipment included in accrued expenses	2,117	$ 2,515
Myonexus Therapeutics, Inc. [Member]
Cash flows from investing activities:
Acquisition of Myonexus Therapeutics, Inc., net of cash acquired	$ (172,556)