Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 130,162	$ 65,897
Short-term investments	166,904	100,138
Prepaid expenses and other current assets	3,382	9,835
Total current assets	300,448	175,870
Operating lease right-of-use assets	20,406	20,963
Property and equipment, net	26,727	24,884
Restricted cash	999	999
Deposit and other long-term assets	19	11
Total assets	348,599	222,727
Current liabilities:
Accounts payable	4,663	4,103
Accrued expenses and other current liabilities	8,079	11,271
Lease liability, current portion	4,025	4,034
Total current liabilities	16,767	19,408
Lease liability, net of current portion	27,753	28,214
Other non-current liabilities	126	148
Total liabilities	44,646	47,770
Stockholders’ equity:
Preferred stock	0	0
Common stock	8	7
Additional paid-in capital	712,713	560,704
Accumulated other comprehensive loss	(833)	(725)
Accumulated deficit	(407,935)	(385,029)
Total stockholders’ equity	303,953	174,957
Total liabilities and stockholders' equity	$ 348,599	$ 222,727