Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Operating activities
Net loss	$ (23,041)	$ (20,299)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,955	1,953
Depreciation expense	491	375
Net (accretion of discount)/amortization of premium on marketable securities	0	(115)
Non-cash interest expense	50	28
Non-cash lease expense	627
Gain on sale of fixed assets, net	(3)	0
Changes in assets and liabilities:
Prepaid expenses and other current assets	298	(221)
Accounts payable	565	97
Accrued expenses and other current liabilities	146	185
Operating lease liabilities	(624)
Other liabilities	21	4
Net cash used in operating activities	(19,515)	(17,993)
Investing activities
Proceeds from sales and maturities of investments	0	31,000
Purchases of property and equipment	(435)	(876)
Proceeds from sale of fixed assets	6	0
Net cash (used in)/provided by investing activities	(429)	30,124
Financing activities
Proceeds from the exercise of stock options	226	258
Net cash provided by financing activities	226	258
Net (decrease) increase in cash, cash equivalents and restricted cash	(19,718)	12,389
Cash, cash equivalents and restricted cash – beginning of period	79,333	94,351
Cash, cash equivalents and restricted cash – end of period	59,615	106,740
Supplemental disclosure of cash flow information
Cash paid for interest	437	215
Noncash investing and financing activities
Property and equipment additions in accounts payable and accrued expenses	$ 406	$ 172