CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 645,361	$ 193,617
Marketable securities	1,045,257	424,185
Investment in equity securities of Regulus Therapeutics Inc.		8,997
Billed and unbilled collaboration receivables	34,002	23,334
Prepaid expenses and other current assets	40,120	21,744
Total current assets	1,764,740	671,877
Marketable securities	13,919	324,799
Property, plant and equipment, net	181,900	114,572
Restricted investments	30,000	150,000
Other assets	4,171	1,562
Total assets	1,994,730	1,262,810
Current liabilities:
Accounts payable	28,355	54,465
Accrued expenses	72,203	42,118
Deferred rent	1,988	1,576
Deferred revenue	41,705	33,540
Total current liabilities	144,251	131,699
Deferred rent, net of current portion	6,626	8,431
Deferred revenue, net of current portion	43,075	49,392
Long-term debt	30,000	150,000
Other liabilities	4,347	3,067
Total liabilities	228,299	342,589
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000,000 shares authorized and no shares issued and outstanding at December 31, 2017 and 2016
Common stock, $0.01 par value per share, 125,000,000 shares authorized; 99,666,549 shares issued and outstanding at December 31, 2017; 85,941,344 shares issued and outstanding at December 31, 2016	997	859
Additional paid-in capital	3,947,552	2,609,614
Accumulated other comprehensive loss	(34,433)	(33,441)
Accumulated deficit	(2,147,685)	(1,656,811)
Total stockholders’ equity	1,766,431	920,221
Total liabilities and stockholders’ equity	$ 1,994,730	$ 1,262,810