Real Estate Charges (Details) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2012 ft²	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	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)			70.00%
Real estate charges	$ (2,801)	$ (80)		$ 24,785	$ (463)
New pre-tax real estate charges				26,700
Previous real estate charges				1,900
Real estate liability restructuring reserve [Abstract]
Balance as of beginning of period				116,064	$ 148,429	$ 148,429
Expense (credit) incurred				(836)		2,258
Payments made				(13,464)		(38,920)
Interest accretion				2,142		4,297
Balance as of end of period	$ 103,906			$ 103,906		$ 116,064