CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 248,334	$ 73,651
Marketable securities	174,076	269,017
Collaboration receivable	11,371	15,048
Prepaid expenses and other current assets	6,318	6,798
Assets held-for-sale	1,324	0
Restricted cash	0	2,412
Total current assets	441,423	366,926
Marketable securities, long-term	27,001	37,222
Property and equipment, net	20,944	29,916
Restricted cash	37,898	20,620
Intangible assets, net	2,883	4,036
Other long-term assets	1,414	711
Total assets	531,563	459,431
Current liabilities:
Accounts payable	9,352	11,456
Accrued expenses	14,060	20,528
Accrued restructuring	3,235	0
Collaboration liabilities	4,721	9,258
Deferred revenue	3,916	2,866
Other current liabilities	16,227	379
Total current liabilities	51,511	44,487
Deferred revenue, net of current portion	1,774	30,751
Other long-term liabilities	17,270	10,039
Total liabilities	70,555	85,277
Commitments and contingencies (Note 15)
Stockholders' Equity:
Common stock, $0.0001 par value per share; 100,000 shares authorized, 98,694 shares issued and 98,464 shares outstanding at December 31, 2018 and 76,584 shares issued and 76,355 shares outstanding at December 31, 2017	10	8
Additional paid-in capital	1,208,025	939,654
Accumulated other comprehensive loss	(87)	(140)
Accumulated deficit	(743,826)	(562,254)
Treasury stock, at cost, 229 shares	(3,114)	(3,114)
Total stockholders' equity	461,008	374,154
Total liabilities and stockholders' equity	$ 531,563	$ 459,431