Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (181,651)	$ (123,564)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	48,808	32,189
Amortization of other intangible assets acquired	151	452
Depreciation and amortization	5,591	2,720
Net amortization/accretion on investment securities	1,437	(3,136)
Non-cash rent expense	1,240	4,827
Benefit from income taxes	0	(176)
Share of losses from equity method investments	376	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	657	86
Other long-term assets	1,975	(2,863)
Accounts payable	1,681	(3,137)
Accrued and other current liabilities	16,175	7,510
Other long-term liabilities	(1,558)	(1,991)
Net cash used in operating activities	(105,118)	(87,083)
Cash flows from investing activities:
Purchases of property and equipment	(48,554)	(36,679)
Proceeds from sales of investments	4,877	0
Proceeds from maturities of investments	371,777	355,765
Purchase of investments	(855,433)	(162,931)
Net cash (used in) provided by investing activities	(527,333)	156,155
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of stock options	7,194	703
Proceeds from issuance of common stock under the employee stock purchase plan	2,844	1,783
Net cash provided by financing activities	620,613	2,486
Net change in cash, cash equivalents and restricted cash	(11,838)	71,558
Cash, cash equivalents and restricted cash — beginning of period	179,425	93,731
Cash, cash equivalents and restricted cash — end of period	167,587	165,289
Non-cash investing activities:
Property and equipment purchases in accounts payable and accrued and other current liabilities	7,909	6,571
Supplemental disclosure:
Cash paid for amounts included in the measurement of lease liabilities	4,236	2,182
Cash received for amounts related to tenant improvement allowances	2,321	2,934
ATM offering
Cash flows from financing activities:
Proceeds from issuance of common stock, net of commissions and issuance costs	14,845	0
Public offering
Cash flows from financing activities:
Proceeds from issuance of common stock, net of commissions and issuance costs	$ 595,730	$ 0