CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 106,279	$ 61,461
Marketable securities	202,679	288,583
Collaboration receivable	45,752	21,185
Prepaid expenses and other current assets	4,816	3,479
Total current assets	359,526	374,708
Property and equipment, net	20,976	21,896
Restricted cash	21,761	20,660
Intangible assets, net	5,478	3,528
Other long-term assets	1,369	248
Total assets	409,110	421,040
Current liabilities:
Accounts payable	9,801	4,053
Accrued expenses	16,539	24,499
Deferred revenue	21,740	9,770
Other current liabilities	83	460
Total current liabilities	48,163	38,782
Deferred revenue, net of current portion	33,310	12,213
Other long-term liabilities	1,858	69
Total liabilities	83,331	51,064
Commitments and contingencies
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, 71,246 shares issued and 71,017 shares outstanding at September 30, 2016 and 69,077 shares issued and 68,958 outstanding at December 31, 2015	7	7
Additional paid-in capital	843,549	824,385
Accumulated other comprehensive income	250	4
Accumulated deficit	(514,914)	(452,372)
Treasury stock, at cost, 229 shares at September 30, 2016 and 119 shares at December 31, 2015	(3,113)	(2,048)
Total stockholders’ equity	325,779	369,976
Total liabilities and stockholders’ equity	$ 409,110	$ 421,040