Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (110,955)	$ (87,407)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,571	1,178
Noncash lease expense	1,391	1,041
Stock-based compensation	16,859	10,295
Accretion of premiums and discounts on investments	(134)	(1,332)
Changes in assets and liabilities:
Accounts receivable	(3,847)	(323)
Unbilled accounts receivable	2,152	(219)
Inventory	(382)
Prepaid expenses and other current assets	(1,408)	(1,381)
Other assets	(66)	(114)
Accounts payable	3,715	982
Accrued expenses	(16,576)	(1,208)
Deferred revenue	(575)	(731)
Operating lease liabilities	(1,073)	(969)
Net cash used in operating activities	(109,328)	(80,188)
Cash flows from investing activities
Purchases of property and equipment	(1,525)	(1,770)
Purchases of investments	(139,250)	(112,916)
Maturities of investments	200,635	204,000
Net cash provided by investing activities	59,860	89,314
Cash flows from financing activities
Proceeds from public offerings of common stock, net of commissions, underwriting discounts and offering costs	308,541
Proceeds from issuance of common stock	1,609	2,039
Other financing activities		(28)
Net cash provided by financing activities	310,150	2,011
Net increase in cash, cash equivalents, and restricted cash	260,682	11,137
Cash, cash equivalents and restricted cash at beginning of period	119,604	73,429
Effect of exchange rate changes on cash, cash equivalents and restricted cash	50	(16)
Cash, cash equivalents and restricted cash at end of period	380,336	84,550
Supplemental cash flow information
Public offering costs incurred but unpaid at period end	118
Property and equipment purchases unpaid at period end	465	1,478
Cash paid for taxes, net	$ 32	$ 53