Investment Securities - Trust Preferred Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Amortized Cost	$ 4,499
Available-for-Sale securities, Fair Value	2,545,470	2,627,831	2,347,766
Reg Div Funding 2004 [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	D
Amortized Cost	3,769
Pooled Trust Preferred Securities One [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Amortized Cost	17,706
Available-for-Sale securities, Fair Value	6,553
Available-for-sale, Unrealized Losses	(11,153)
Realized Losses 2015	0
Pooled Trust Preferred Securities One [Member] | Reg Div Funding 2004 [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Pooled trust preferred securities, Class	B-2
Lowest Credit Rating	D
Amortized Cost	3,769
Available-for-Sale securities, Fair Value	221
Available-for-sale, Unrealized Losses	(3,548)
Realized Losses 2015	0
# of Issuers Currently Performing	24
# of Issuers Currently Remaining	42
Actual Deferrals and Defaults as a Percent of Original Collateral	34.20%
Expected Defaults as a % of Remaining Performing Collateral	8.90%
Excess Subordination as a % of Current Performing Collateral	0.00%
Pooled Trust Preferred Securities One [Member] | Pretsl XXVII LTD [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Pooled trust preferred securities, Class	B
Lowest Credit Rating	B
Amortized Cost	4,491
Available-for-Sale securities, Fair Value	2,520
Available-for-sale, Unrealized Losses	(1,971)
Realized Losses 2015	0
# of Issuers Currently Performing	34
# of Issuers Currently Remaining	46
Actual Deferrals and Defaults as a Percent of Original Collateral	22.70%
Expected Defaults as a % of Remaining Performing Collateral	5.20%
Excess Subordination as a % of Current Performing Collateral	41.10%
Pooled Trust Preferred Securities One [Member] | Trapeza Ser 13A [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Pooled trust preferred securities, Class	A2A
Lowest Credit Rating	B+
Amortized Cost	9,446
Available-for-Sale securities, Fair Value	3,812
Available-for-sale, Unrealized Losses	(5,634)
Realized Losses 2015	0
# of Issuers Currently Performing	48
# of Issuers Currently Remaining	59
Actual Deferrals and Defaults as a Percent of Original Collateral	15.00%
Expected Defaults as a % of Remaining Performing Collateral	2.70%
Excess Subordination as a % of Current Performing Collateral	51.90%
Single Issuer Trust Preferred Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Amortized Cost	13,561
Available-for-Sale securities, Fair Value	12,774
Available-for-sale, Unrealized Losses	(787)
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | First Empire Cap (M&T) [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BB+
Amortized Cost	961
Available-for-Sale securities, Fair Value	1,009
Available-for-sale, Unrealized Losses	48
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | First Empire Cap (M&T) [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BB+
Amortized Cost	2,917
Available-for-Sale securities, Fair Value	3,027
Available-for-sale, Unrealized Losses	110
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | Fleet Cap Tr V (BOA) [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BB
Amortized Cost	3,383
Available-for-Sale securities, Fair Value	2,888
Available-for-sale, Unrealized Losses	(495)
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | J P Morgan Chase Cap XIII [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BBB-
Amortized Cost	4,748
Available-for-Sale securities, Fair Value	4,175
Available-for-sale, Unrealized Losses	(573)
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | NB-Global [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BB
Amortized Cost	755
Available-for-Sale securities, Fair Value	825
Available-for-sale, Unrealized Losses	70
Realized Losses 2015	0
Single Issuer Trust Preferred Securities [Member] | Chase Cap II [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Lowest Credit Rating	BBB-
Amortized Cost	797
Available-for-Sale securities, Fair Value	850
Available-for-sale, Unrealized Losses	53
Realized Losses 2015	0
Trust Preferred Securities [Member]
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Amortized Cost	31,267
Available-for-Sale securities, Fair Value	19,327
Available-for-sale, Unrealized Losses	(11,940)
Realized Losses 2015	$ 0