Federal, State and Local Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Federal corporate income tax rate		35.00%	35.00%	35.00%
Income tax benefit due to change in tax rate		$ 42,000,000
Total assets		$ 49,124,195,000	$ 48,926,555,000	$ 50,317,796,000
Percentage of alternative tax on apportioned capital		0.15%
Alternative tax capped value, New York State		$ 5,000,000
Alternative tax - phased out period		6 years
Outstanding amount of the investment		$ 46,200,000	42,400,000
Other commitments of additional anticipated equity contributions relating to current investments		$ 23,900,000	21,900,000
Commitments period		4 years
Affordable housing tax credits and other tax benefits recognized		$ 4,500,000	4,000,000	3,200,000
Affordable housing tax credits and other tax benefits, related amortization recognized		3,100,000	3,000,000	2,400,000
Affordable housing tax credits and other tax benefits, impairment losses		0	0	0
Unrecognized gross tax benefits		33,681,000	33,487,000	30,456,000	$ 24,779,000
Total amount of net unrecognized tax benefits that would affect the effective tax rate, if recognized		26,600,000
Income tax benefit attributed to interest and penalties		1,800,000	1,200,000	$ 1,100,000
Accrued interest and penalties on tax liabilities		8,900,000	6,900,000
Net deferred tax liabilities		$ 84,797,000	$ 32,611,000
Scenario, Forecast
Income Taxes [Line Items]
Federal corporate income tax rate	21.00%
Assets for disallowance of deduction for FDIC premium	$ 50,000,000,000
Percentage of limitations on NOL carryforwards to taxable income	80.00%
Minimum
Income Taxes [Line Items]
Dividends received deduction		70.00%
Minimum | Scenario, Forecast
Income Taxes [Line Items]
Dividends received deduction	50.00%
Maximum
Income Taxes [Line Items]
Dividends received deduction		80.00%
Estimated change in balance of unrecognized tax benefit, within next twelve months		$ 20,000,000
Maximum | Scenario, Forecast
Income Taxes [Line Items]
Dividends received deduction	65.00%
New York State Division of Taxation and Finance
Income Taxes [Line Items]
Effective tax rate			6.50%	7.10%
New York City
Income Taxes [Line Items]
Net operating loss carryforward		$ 44,900,000
Operating loss carryforward, expiration year		2035
Alternative tax capped value, New York State		$ 10,000,000
New York City | Financial institutions with total assets below $100 billion
Income Taxes [Line Items]
Effective tax rate			8.85%	9.00%
New York City | Tax benefit on Interest income earned or situated in low-income communities phased out for financial institutions with total assets | Minimum
Income Taxes [Line Items]
Total assets		100,000,000,000
New York City | Tax benefit on Interest income earned or situated in low-income communities phased out for financial institutions with total assets | Maximum
Income Taxes [Line Items]
Total assets		150,000,000,000
Special Federal Tax Provision
Income Taxes [Line Items]
Tax bad debt base-year reserves		61,500,000
Net deferred tax liabilities		$ 12,900,000