CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (161,867)	$ (103,227)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	2,068	286
Share-based compensation expense	15,080	5,701
Class A common shares issued or to be issued as consideration for Primatope, including milestone payments	8,800
Loss on disposal of property and equipment	21	66
Other		235
Non-cash lease expense	1,211
Accretion of discounts on short-term investments	(3,501)	(1,423)
Deferred income taxes	(3,156)	(978)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,020)	(4,791)
Accounts payable	(4,705)	8,823
Accrued expenses and other liabilities	4,638	9,296
Accrued milestones	(15,000)	5,000
Operating lease liabilities	(1,264)
Other long-term liabilities	326
Net cash used in operating activities	(158,369)	(81,012)
Cash flows from investing activities:
Purchases of property and equipment	(3,203)	(5,290)
Purchases of short-term investments	(488,773)	(402,008)
Proceeds from the maturities of short-term investments	541,190	168,100
Net cash provided by (used in) investing activities	49,214	(239,198)
Cash flows from financing activities:
Payments of offering costs	(118)	(3,657)
Proceeds from exercise of options and employee share purchase plan	1,119	377
Net cash provided by financing activities	84,107	346,736
Net increase in cash and cash equivalents and restricted cash	(25,048)	26,526
Cash, cash equivalents and restricted cash at beginning of period	72,186	45,660
Cash, cash equivalents and restricted cash at end of period	47,138	72,186
Supplemental information:
Cash paid for income taxes	1,724	383
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs included in accrued expenses and accounts payable		404
Property and equipment included in accrued expenses and accounts payable	222	1,292
Series C convertible preferred shares
Cash flows from financing activities:
Proceeds from issuance of convertible preferred shares, net of issuance costs		190,822
Initial Public Offering | Class A common shares
Cash flows from financing activities:
Proceeds from issuance of common shares, net of underwriting commissions and discounts		$ 159,194
Follow-On Offering | Class A common shares
Cash flows from financing activities:
Proceeds from issuance of common shares, net of underwriting commissions and discounts	48,595
Private Placement | Class A1 common shares
Cash flows from financing activities:
Proceeds from issuance of common shares from private placement, net of underwriting commissions and discounts	$ 34,511