Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 155,446	$ 120,320
Short-term marketable securities	454,890	459,256
Accounts receivable, net	7,384	0
Inventory	1,389	0
Prepaid expenses and other current assets	13,977	13,832
Total current assets	633,086	593,408
Long-term marketable securities	21,431	0
Long-term investments—restricted	2,125	1,510
Property and equipment, net	9,567	6,333
Operating lease assets	20,096	21,158
Total assets	686,305	622,409
Current liabilities:
Accounts payable	12,582	19,575
Accrued expenses and other current liabilities	37,333	38,716
Operating lease liabilities	1,424	1,747
Total current liabilities	51,339	60,038
Operating lease liabilities, net of current portion	15,282	15,904
Total liabilities	66,621	75,942
Commitments and contingencies (Note 6)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 5,000,000 shares authorized; no shares issued or outstanding	0	0
Common stock, $0.01 par value per share; 125,000,000 shares authorized; 56,081,993 shares and 51,617,639 shares issued and outstanding as of June 30, 2020 and December 31, 2019, respectively	561	516
Additional paid-in capital	1,247,158	1,033,819
Accumulated other comprehensive income (loss)	(8)	111
Accumulated deficit	(628,027)	(487,979)
Total stockholders' equity	619,684	546,467
Total liabilities and stockholders' equity	$ 686,305	$ 622,409