Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (111,144)	$ (77,677)	$ (155,645)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,514	1,564	3,216
Share-based compensation	22,014	23,585	26,062
Restructuring share-based compensation	0	0	948
Deferred income taxes	(1,688)	(1,248)	(1,589)
Interest expense under build-to-suit lease obligation	0	0	3,696
Amortization of right-of-use assets	5,463	5,256	0
Loss from disposal of fixed assets	0	0	584
Changes in operating assets and liabilities:
Accounts receivable	53	0	238
Prepaid and other assets	799	807	9,139
Deferred revenue	0	0	110,242
Accounts payable, accruals and other liabilities	7,728	(78)	(25,628)
Restructuring liability	0	(461)	461
Operating lease liabilities	5,101	4,717	0
Net cash used in operating activities	(80,362)	(52,969)	(28,276)
Investing activities
Purchases of property and equipment	(196)	(555)	(1,768)
Proceeds from disposal of fixed assets	0	8	39
Net cash used in investing activities	(196)	(547)	(1,729)
Financing activities
Proceeds from subscription of ordinary shares	0	0	39,758
Proceeds from issuance of ordinary shares upon exercise of stock options	215	228	4,686
Reduction of build-to-suit lease obligation	0	0	(4,400)
Net cash provided by financing activities	215	228	40,044
Net increase (decrease) in cash, cash equivalents and restricted cash	(80,343)	(53,288)	10,039
Cash, cash equivalents and restricted cash, beginning of the year	378,427	431,715	421,676
Cash, cash equivalents and restricted cash, end of the period	298,084	378,427	431,715
Total cash, cash equivalents and restricted cash, end of the period	298,084	431,715	421,676
Supplemental disclosures of cash flow information
Cash paid (refunds received) for income taxes, net	1,367	1,580	(995)
Supplemental disclosures of non-cash investing and financing activities
Acquisition of property and equipment included in accounts payable and accrued liabilities	0	5	90
Right-of-use assets recorded upon adoption of ASC 842	0	28,530	0
Reduction of build-to-suit lease obligation upon adoption of ASC 842	0	51,546	0
Reduction of amounts capitalized under build-to-suit lease upon adoption of ASC 842	0	46,760	0
Reduction of capitalized interest under build-to-suit lease upon adoption of ASC 842	$ 0	$ 1,099	$ 0