Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net income (loss)	$ 66,858	$ (164,981)	$ (68,357)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	4,725	3,519	3,024
Equity-based compensation	44,057	34,985	18,873
Loss from equity method investment in Casebia	5,467	4,275	1,763
Non-cash expense related to ViaCyte transaction		15,582
Gain from consolidation of Casebia	(16,000)
Other income, non-cash		(169)	(9)
Changes in:
Accounts receivable	(11)	2,538	531
Prepaid expenses and other assets	(32,618)	(3,342)	(4,117)
Accounts payable and accrued expenses	5,025	12,110	(831)
Deferred revenue	(45,146)	(296)	(20,718)
Deferred rent		(709)	(522)
Operating lease assets and liabilities	(663)
Other liabilities, net	24,983	249	270
Net cash provided by (used in) operating activities	56,677	(96,239)	(70,093)
Investing activities
Purchase of property and equipment	(6,684)	(2,773)	(7,814)
Net cash and restricted cash received in connection with the acquisition of Casebia	8,009
Purchase of available for sale debt security			(500)
Net cash provided by (used in) investing activities	1,325	(2,773)	(8,314)
Financing activities
Proceeds from issuance of common shares, net of issuance costs	415,019	307,053
Proceeds from exercise of options, net of issuance costs	15,964	8,938	2,608
Repurchase of treasury shares		(57)
Net cash provided by financing activities	430,983	315,934	2,608
Effect of exchange rate changes on cash	15	(22)	41
Increase in cash	489,000	216,900	(75,758)
Cash, cash equivalents and restricted cash, beginning of period	459,812	242,912	318,670
Cash, cash equivalents and restricted cash, end of period	948,812	459,812	242,912
Supplemental disclosure of non-cash investing and financing activities
Property and equipment purchases in accounts payable and accrued expenses	1,811	334
Stock option issuance costs included in accrued expenses	$ 295	$ 375
Costs for proposed supplemental offering in accounts payable and accrued expenses			$ 290