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Federal, State and Local Taxes - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Income Taxes [Line Items]        
Outstanding amount of the investment $ 42,400,000 $ 35,400,000    
Other commitments of additional anticipated equity contributions relating to current investments $ 21,900,000 18,300,000    
Commitments period 4 years      
Effect of adopting Accounting Standards Update 2014-01     $ (1,303,000)  
Affordable housing tax credits and other tax benefits recognized $ 4,000,000 3,200,000    
Affordable housing tax credits and other tax benefits, related amortization recognized 3,000,000 2,400,000    
Affordable housing tax credits and other tax benefits, impairment losses 0 0    
Total assets $ 48,926,555,000 50,317,796,000 48,559,217,000  
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      
Unrecognized gross tax benefits $ 33,487,000 30,456,000 24,779,000 $ 20,250,000
Total amount of net unrecognized tax benefits that would affect the effective tax rate, if recognized 21,800,000      
Income tax benefit attributed to interest and penalties 1,200,000 1,100,000 $ 700,000  
Accrued interest and penalties on tax liabilities 6,900,000 $ 5,000,000    
Net deferred tax liabilities 32,611,000      
Maximum        
Income Taxes [Line Items]        
Estimated change in balance of unrecognized tax benefit, within next twelve months (14,000,000)      
New York City        
Income Taxes [Line Items]        
Net operating loss carryforward $ 354,900,000      
Operating loss carryforward, expiration year 2035      
Alternative tax capped value, New York State $ 10,000,000      
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      
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 | Financial institutions with total assets below $100 billion        
Income Taxes [Line Items]        
Effective tax rate 8.85% 9.00%    
New York State Division of Taxation and Finance        
Income Taxes [Line Items]        
Effective tax rate 6.50% 7.10%    
Special Federal Tax Provision        
Income Taxes [Line Items]        
Tax bad debt base-year reserves $ 61,500,000      
Net deferred tax liabilities $ 21,500,000