Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 346,629	$ 327,214
Marketable securities	564,054	779,246
Prepaid expenses	40,209	32,888
Receivables and other current assets	16,575	12,826
Total current assets	967,467	1,152,174
Marketable securities	107,674	131,506
Property, plant and equipment, net	153,920	151,176
Intangible assets, net	13,254	14,326
Goodwill	13,128	13,128
Operating lease right-of-use assets	194,469	185,885
Restricted cash and other non-current assets	79,192	79,229
Total assets	1,529,104	1,727,424
Current liabilities:
Accounts payable	30,527	42,995
Accrued expenses and other current liabilities	118,091	141,556
Operating lease liability, current portion	20,380	20,175
Deferred revenue, current portion	6,355	8,474
Collaboration research advancement, current portion	9,069	10,380
Total current liabilities	184,422	223,580
Deferred revenue, net of current portion	9,791	9,791
Collaboration research advancement, net of current portion	26,843	27,834
Contingent consideration	4,869	7,977
Operating lease liability, net of current portion	179,962	170,812
Other non-current liabilities	2,784	2,437
Total liabilities	408,671	442,431
Commitments and contingencies (Note 8)
Stockholders’ equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2020 and December 31, 2019	0	0
Common stock, $0.01 par value, 125,000 shares authorized; 55,620 and 55,368 shares issued and outstanding at March 31, 2020 and December 31, 2019, respectively	556	554
Additional paid-in capital	3,607,139	3,568,184
Accumulated other comprehensive loss	(2,799)	(1,893)
Accumulated deficit	(2,484,463)	(2,281,852)
Total stockholders’ equity	1,120,433	1,284,993
Total liabilities and stockholders’ equity	$ 1,529,104	$ 1,727,424