Real Estate Charges (Details) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2012 ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2010 ft² office_location
Restructuring and Related Activities [Abstract]
Area of office space to be sub-leased (in square feet) | ft²			510,000		380,000
Consolidated number of office locations in New York | office_location					2
Number of office locations | office_location					3
Portion of office space to be subleased in New York (more than 70%)			70.00%
Real estate charges	$ 27,586	$ (383)
New pre-tax real estate charges	28,500
Real estate liability restructuring reserve [Abstract]
Balance as of beginning of period	116,064	$ 148,429		$ 148,429
Expense (credit) incurred	(391)			2,258
Payments made	(5,289)			(38,920)
Interest accretion	1,075			4,297
Balance as of end of period	$ 111,459			$ 116,064