CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating Activities:
Net loss	$ (25,864)	$ (43,218)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	925	1,939
Loss on disposal of property and equipment	0	88
Amortization of debt issuance costs	356	356
Non-cash stock-based compensation	3,965	5,558
Other	0	(14)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	4,521	(296)
Accounts payable and accrued expenses	(8,450)	(11,853)
Deferred revenue	1,437	(3,167)
Net cash used in operating activities	(23,110)	(50,607)
Investing Activities:
Capital expenditures	(122)	(805)
Proceeds from maturities of marketable securities	0	22,000
Purchases of marketable securities	(57,606)	(2,484)
Net cash provided by (used in) investing activities	(57,728)	18,711
Financing Activities:
Net proceeds from sales of common stock	185,918	55,239
Proceeds from the exercise of stock options and employee stock purchases	5	942
Net cash provided by financing activities	185,923	56,181
Effect of exchange rate on cash, cash equivalents and restricted cash	(73)	(45)
Net increase in cash, cash equivalents and restricted cash	105,012	24,240
Cash, cash equivalents and restricted cash at beginning of period	82,180	81,959
Cash, cash equivalents and restricted cash at end of period	187,192	106,199
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	125	194
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 6,094	$ 6,094