Office Facilities - Summary of Office Facilities Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Depreciation and amortization of furniture, equipment and leasehold improvements	$ 6,788	$ 7,188	$ 7,748
Office facilities, gross	111,306	133,097
Less accumulated depreciation	(84,073)	(104,812)
Total	27,233	28,285
Furniture, fixtures and equipment
Property, Plant and Equipment [Line Items]
Office facilities, gross	55,210	75,704
Leasehold improvements
Property, Plant and Equipment [Line Items]
Office facilities, gross	$ 56,096	$ 57,393