Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 199,444	$ 126,705
Marketable securities	673,313	881,688
Prepaid expenses and other current assets	25,479	26,700
Total current assets	898,236	1,035,093
Property and equipment, net	8,684	9,126
Restricted cash	2,367	2,367
Right-of-use operating asset	31,992	33,771
Other long-term assets	3,694	3,793
Total assets	944,973	1,084,150
Current liabilities:
Accounts payable	7,910	15,266
Accrued expenses	52,180	86,618
Operating lease liability, current portion	10,270	10,244
Total current liabilities	70,360	112,128
Operating lease liability, net of current portion	24,951	26,848
Other liabilities	456	519
Total liabilities	95,767	139,495
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at March 31, 2020 and December 31, 2019; no shares issued or outstanding at March 31, 2020 and December 31, 2019
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at March 31, 2020 and December 31, 2019; 51,920,852 and 51,880,227 shares issued at March 31, 2020 and December 31, 2019; 51,917,819 and 51,877,194 shares outstanding at March 31, 2020 and December 31, 2019	5	5
Treasury stock, at cost, 3,033 shares at March 31, 2020 and December 31, 2019	(400)	(400)
Additional paid-in capital	2,620,700	2,587,322
Accumulated deficit	(1,770,307)	(1,643,567)
Accumulated other comprehensive gain (loss)	(792)	1,295
Total stockholders’ equity	849,206	944,655
Total liabilities and stockholders’ equity	$ 944,973	$ 1,084,150