CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (18,672)	$ (12,483)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	84	36
Stock-based compensation expense	1,876	1,836
Loss on disposal of fixed assets		42
Noncash lease expense	62	46
Noncash lease liability	95	(55)
Amortization of premium on investments	1	(1)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	258	(847)
Accounts payable and accrued expenses	2,259	(238)
Net cash used in operating activities	(14,037)	(11,664)
Cash flows from investing activities
Maturities of short-term investments	1,737	5,000
Purchases of short-term investments	(8,433)
Deposit on property and equipment		(80)
Purchases of property and equipment	(1)	(52)
Net cash provided by investing activities	(6,697)	4,868
Cash flows from financing activities
Proceeds from exercise of stock options	312	65
Financing costs	(195)	(148)
Net cash provided by/(used in) financing activities	117	(83)
Net decrease in cash and cash equivalents	(20,617)	(6,879)
Cash and cash equivalents—beginning of year	90,943	67,727
Cash and cash equivalents—end of year	$ 70,326	60,848
Supplemental disclosure of cash flow information
Property and equipment in accounts payable and accrued expenses		48
Operating lease liability		3,357
Operating right-of-use asset		$ 2,458