Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Examination [Line Items]
New York City unincorporated business tax rate	4.00%
Interest expense recorded in income tax expense	$ 700,000	$ 400,000	$ 400,000
Accrued interest payable recorded on the consolidated statements of financial condition	1,700,000	1,000,000	600,000
Accrued penalties recorded on the consolidated statements of financial condition	$ 0	0	0
Minimum years that remain open and may be subject to examination vary under local law	1 year
Maximum years that remain open and may be subject to examination vary under local law	7 years
Unrecognized tax benefits	$ 12,596,000	$ 12,004,000	$ 11,311,000	$ 2,975,000
Accumulated undistributed earnings	683,000,000
Additional taxes not provided	54,800,000
City of New York [Member]
Income Tax Examination [Line Items]
Unrecognized tax benefits	$ 6,600,000