Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 342,295	$ 190,943
Marketable securities	1,008,956	731,833
Prepaid expenses and other current assets	20,281	21,919
Total current assets	1,371,532	944,695
Property and equipment, net	6,513	5,643
Restricted cash	2,367	2,367
Right of use operating asset	38,124
Other long-term assets	4,378
Total assets	1,422,914	952,705
Current liabilities:
Accounts payable	13,556	34,036
Accrued expenses	47,651	51,994
Other current liabilities	7,169
Total current liabilities	68,376	86,030
Long-term lease operating liability, net of current portion	34,528
Other long-term liabilities	476	3,704
Total liabilities	103,380	89,734
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.0001 par value per share; 5,000,000 shares authorized at March 31, 2019 and December 31, 2018; no shares issued or outstanding at March 31, 2019 and December 31, 2018
Common stock, $0.0001 par value per share; 120,000,000 shares authorized at March 31, 2019 and December 31, 2018; 51,037,205 and 46,891,296 shares issued at March 31, 2019 and December 31, 2018; 51,034,172 and 46,888,263 shares outstanding at March 31, 2019 and December 31, 2018	5	5
Treasury stock, at cost, 3,033 shares at March 31, 2019 and December 31, 2018	(400)	(211)
Additional paid-in capital	2,446,770	1,827,021
Accumulated deficit	(1,126,735)	(963,329)
Accumulated other comprehensive loss	(106)	(515)
Total stockholders’ equity	1,319,534	862,971
Total liabilities and stockholders’ equity	$ 1,422,914	$ 952,705