Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 79,449	$ 77,123
Short-term marketable securities	335,907	387,174
Prepaid expenses and other current assets	14,675	16,539
Total current assets	430,031	480,836
Long-term marketable securities	39,886	147,881
Property and equipment, net	46,732	25,162
Operating lease right-of-use asset	33,923
Other non-current assets	2,659	8,105
Total assets	553,231	661,984
Current liabilities:
Accounts payable	2,590	1,891
Accrued expenses and other current liabilities	24,015	19,468
Contract liabilities	18,739	11,427
Total current liabilities	45,344	32,786
Contract liabilities, less current portion	43,753	57,350
Operating lease liability, less current portion	68,865
Deferred rent, less current portion		24,532
Other non-current liabilities	379	471
Total liabilities	158,341	115,139
Commitments and contingencies
Stockholders' equity:
Convertible preferred stock, $0.01 par value; 40,000,000 shares authorized as of December 31, 2019 and December 31, 2018; 0 shares issued and outstanding as of December 31, 2019 and December 31, 2018	0	0
Common stock, $0.01 par value; 400,000,000 shares authorized as of December 31, 2019 and December 31, 2018; 96,189,935 and 94,662,435 shares issued and outstanding as of December 31, 2019 and December 31, 2018, respectively	1,288	1,273
Additional paid-in capital	818,803	774,158
Accumulated other comprehensive income (loss)	350	(649)
Accumulated deficit	(425,551)	(227,937)
Total stockholders’ equity	394,890	546,845
Total liabilities and stockholders’ equity	$ 553,231	$ 661,984