CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 150,738	$ 61,461
Marketable securities	202,413	288,583
Collaboration receivable	70,242	21,185
Prepaid expenses and other current assets	4,607	3,479
Total current assets	428,000	374,708
Property and equipment, net	20,847	21,896
Restricted cash	21,761	20,660
Intangible assets, net	5,189	3,528
Other long-term assets	1,940	248
Total assets	477,737	421,040
Current liabilities:
Accounts payable	3,632	4,053
Accrued expenses	26,866	24,499
Collaboration advance	32,895	0
Deferred revenue	7,272	9,770
Other current liabilities	11	460
Total current liabilities	70,676	38,782
Deferred revenue, net of current portion	31,360	12,213
Other long-term liabilities	3,793	69
Total liabilities	105,829	51,064
Commitments and contingencies (Note 14)
Stockholders' Equity:
Preferred stock, $0.01 par value per share; 5,000 shares authorized, 100 shares of Series A Junior Participating Preferred Stock, $0.01 par value per share designated and no shares issued and outstanding	0	0
Common stock, $0.0001 par value per share; 100,000 shares authorized, 71,305 shares issued and 71,076 shares outstanding at December 31, 2016 and 69,077 shares issued and 68,958 shares outstanding at December 31, 2015	7	7
Additional paid-in capital	848,304	824,385
Accumulated other comprehensive income	86	4
Accumulated deficit	(473,375)	(452,372)
Treasury stock, at cost, 229 shares and 119 shares at December 31, 2016 and December 31, 2015, respectively	(3,114)	(2,048)
Total stockholders' equity	371,908	369,976
Total liabilities and stockholders' equity	$ 477,737	$ 421,040