Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net loss	$ (168,312)	$ (353,046)
Adjustments to reconcile net loss to cash flows from operating activities:
Gain from sale of Priority Review Voucher, net of commission	(108,069)
Acquired in-process research and development		173,240
Depreciation and amortization	13,004	11,113
Reduction in the carrying amounts of the right of use assets	5,389	2,951
Amortization of investment discount	(1,928)	(5,800)
Non-cash interest expense	12,217	10,513
Stock-based compensation	51,640	35,901
Other	(800)	892
Changes in operating assets and liabilities, net:
Net increase in accounts receivable	(13,149)	(7,937)
Net increase in inventory	(8,271)	(31,124)
Net increase in other assets	(44,309)	(87,708)
Net increase in deferred revenue	794,484
Net (decrease) increase in accounts payable, accrued expenses and other liabilities	(11,709)	25,768
Net cash provided by (used in) operating activities	520,187	(225,237)
Cash flows from investing activities:
Purchase of property and equipment	(28,289)	(32,945)
Proceeds from sale of Priority Review Voucher, net of commission	108,069
Purchase of available-for-sale securities	(756,738)	(731,288)
Maturity and sale of available-for-sale securities	626,980	1,225,847
Acquisition of Myonexus Therapeutics, Inc., net of cash acquired		(172,556)
Other	(1,927)	(1,454)
Net cash (used in) provided by investing activities	(51,905)	287,604
Cash flows from financing activities:
Proceeds from issuance of common stock to Roche, net of offering costs		365,353
Proceeds from exercise of stock options and purchase of stock under the Employee Stock Purchase Program	29,342	19,391
Taxes paid related to net share settlement of equity awards	(4,798)	(889)
Net cash provided by financing activities	336,597	383,855
Increase in cash, cash equivalents and restricted cash	804,879	446,222
Cash, cash equivalents and restricted cash:
Beginning of period	843,645	370,829
End of period	1,648,524	817,051
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	1,639,959	808,591
Restricted cash in other assets	$ 8,565	$ 8,460
Restricted Cash, Noncurrent, Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent	us-gaap:OtherAssetsNoncurrent
Total cash, cash equivalents and restricted cash	$ 1,648,524	$ 817,051
Supplemental disclosure of cash flow information:
Cash paid during the period for interest	15,032	4,275
Supplemental schedule of non-cash investing activities and financing activities:
Right of use asset and lease liability additions	37,586
Sale of available-for-sale securities included in investment receivable		20,000
Intangible assets and property and equipment included in accrued expenses	9,032	$ 3,128
Roche
Cash flows from financing activities:
Proceeds from issuance of common stock to Roche, net of offering costs	$ 312,053