Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (43,693)	$ (41,240)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	4,048	4,088
Depreciation expense	1,031	803
Net (accretion of discount)/amortization of premium on marketable securities	0	(161)
Non-cash interest expense	132	51
Non-cash lease expense	1,117
Gain on sale of fixed assets, net	(5)	0
Changes in assets and liabilities:
Prepaid expenses and other current assets	632	(144)
Accounts payable	2,812	1,324
Accrued expenses and other current liabilities	(1,001)	1,920
Operating lease liabilities	(1,111)
Other liabilities	147	10
Net cash used in operating activities	(35,891)	(33,349)
Investing activities
Proceeds from sales and maturities of investments	0	51,000
Purchases of property and equipment	(651)	(1,480)
Proceeds from sale of fixed assets	6	0
Net cash (used in)/provided by investing activities	(645)	49,520
Financing activities
Payment of deferred offering costs	0	(56)
Proceeds from issuance of common stock, net of issuance cost	48,641	0
Proceeds from the exercise of stock options	235	259
Net cash provided by financing activities	48,876	203
Net (decrease) increase in cash, cash equivalents and restricted cash	12,340	16,374
Cash, cash equivalents and restricted cash – beginning of period	79,333	94,351
Cash, cash equivalents and restricted cash – end of period	91,673	110,725
Supplemental disclosure of cash flow information
Cash paid for interest	875	436
Cash paid for taxes	20	0
Noncash investing and financing activities
Deferred financing and public offering costs in accounts payable and accrued expenses	234	46
Property and equipment additions in accounts payable and accrued expenses	$ 248	$ 211