Actual Capital Amounts and Ratios for Commercial Bank in Comparison to Minimum Requirement for Capital Adequacy Purposes (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Total regulatory capital, Leverage Capital Amount
Total regulatory capital, Leverage Capital Amount	$ 3,580,302	$ 3,503,672
Minimum for capital adequacy purposes, Leverage Capital Amount	1,575,464	1,544,875
Excess, Leverage Capital Amount	2,004,838	1,958,797
Leverage Capital Ratio
Total regulatory capital, Leverage Capital Ratio	9.09%	9.07%
Minimum for capital adequacy purposes, Leverage Capital Ratio	4.00%	4.00%
Excess, Leverage Capital Ratio	5.09%	5.07%
Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	3,580,302	3,503,672
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	1,054,144	1,023,848
Excess, Risk-Based Capital, Tier 1 Amount	2,526,158	2,479,824
Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	13.59%	13.69%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	4.00%	4.00%
Excess, Risk-Based Capital, Tier 1 Ratio	9.59%	9.69%
Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	3,750,915	3,674,679
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	2,108,287	2,047,696
Excess, Risk-Based Capital, Total Amount	1,642,628	1,626,983
Total regulatory capital, Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	14.23%	14.36%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	6.23%	6.36%
New York Commercial Bank
Total regulatory capital, Leverage Capital Amount
Total regulatory capital, Leverage Capital Amount	322,611	285,267
Minimum for capital adequacy purposes, Leverage Capital Amount	99,219	89,815
Excess, Leverage Capital Amount	223,392	195,452
Leverage Capital Ratio
Total regulatory capital, Leverage Capital Ratio	13.01%	12.70%
Minimum for capital adequacy purposes, Leverage Capital Ratio	4.00%	4.00%
Excess, Leverage Capital Ratio	9.01%	8.70%
Tier 1 Amount
Total regulatory capital, Risk-Based Capital, Tier 1 Amount	322,611	285,267
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Amount	75,862	69,650
Excess, Risk-Based Capital, Tier 1 Amount	246,749	215,617
Tier 1 Ratio
Total regulatory capital, Risk-Based Capital, Tier 1 Ratio	17.01%	16.38%
Minimum for capital adequacy purposes, Risk-Based Capital, Tier 1 Ratio	4.00%	4.00%
Excess, Risk-Based Capital, Tier 1 Ratio	13.01%	12.38%
Total Amount
Total regulatory capital, Risk-Based Capital, Total Amount	335,509	301,683
Minimum for capital adequacy purposes, Risk-Based Capital, Total Amount	151,724	139,300
Excess, Risk-Based Capital, Total Amount	$ 183,785	$ 162,383
Total regulatory capital, Risk-Based Capital, Total Ratio
Total regulatory capital, Risk-Based Capital, Total Ratio	17.69%	17.33%
Minimum for capital adequacy purposes, Risk-Based Capital, Total Ratio	8.00%	8.00%
Excess, Risk-Based Capital, Total Ratio	9.69%	9.33%