Condensed Statement of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (54,480)	$ (31,586)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Stock-based compensation	14,215	7,867
Amortization of other intangible assets acquired	151	151
Depreciation and amortization	1,893	544
Net amortization/accretion on investment securities	(207)	(1,223)
Non-cash rent expense	718	1,275
Benefit from income taxes	0	(50)
Share of losses from equity method investments	64	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	2,552	(1,892)
Other long-term assets	(57)	(188)
Accounts payable	(1,044)	(348)
Accrued and other current liabilities	(3,913)	(4,095)
Other long-term liabilities	(701)	(711)
Net cash used in operating activities	(40,809)	(30,256)
Cash flows from investing activities:
Purchases of property and equipment	(12,253)	(10,423)
Proceeds from maturities of investments	120,261	95,708
Purchase of investments	(123,015)	(52,397)
Net cash (used in) provided by investing activities	(15,007)	32,888
Cash flows from financing activities:
Proceeds from issuance of common stock, net of commissions and issuance costs	14,845	0
Proceeds from issuance of common stock and upon exercise of stock options	303	0
Proceeds from issuance of common stock under the employee stock purchase plan	1,438	684
Net cash provided by financing activities	16,586	684
Net change in cash, cash equivalents and restricted cash	(39,230)	3,316
Cash, cash equivalents and restricted cash — beginning of period	179,425	93,731
Cash, cash equivalents and restricted cash — end of period	140,195	97,047
Non-cash investing activities:
Property and equipment purchases in accounts payable and accrued liabilities	4,208	5,134
Supplemental disclosure:
Cash paid for amounts included in the measurement of lease liabilities	1,396	391
Cash received for amounts related to tenant improvement allowances	$ 532	$ 0