Fair Values Of Assets And Liabilities (Summary Of Balances Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	$ 1,949,697	$ 2,176,290	$ 1,870,831
Trading account securities	1,068	497	1,036
Derivative assets	37,239	37,956	46,653
Derivative liabilities	34,990	34,807	50,262
US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	340,178	336,095	217,645
U.S. Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	828,275	895,688	973,715
Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	175,300	152,716	110,259
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	39,772	36,386	32,324	30,770
Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	417,303	605,225	368,282
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	53,574	51,528	52,057
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	23,438	22,163	24,470	22,169
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,068	497	1,036
Mortgage loans held-for-sale	215,231	332,485	370,570
Mortgage servicing rights	8,719	8,946	7,344
Nonqualified deferred compensation assets	7,783	7,222	6,545
Derivative assets	51,529	48,221	52,436
Total	2,234,027	2,573,661	2,308,762
Derivative liabilities	37,797	37,264	54,745
Fair Value, Measurements, Recurring [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	340,178	336,095	217,645
Fair Value, Measurements, Recurring [Member] | U.S. Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	828,275	895,688	973,715
Fair Value, Measurements, Recurring [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	175,300	152,716	110,259
Fair Value, Measurements, Recurring [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	135,067	135,038	148,873
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	417,303	605,225	368,282
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	53,574	51,528	52,057
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities
Mortgage loans held-for-sale
Mortgage servicing rights
Nonqualified deferred compensation assets
Derivative assets
Total
Derivative liabilities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,068	497	1,036
Mortgage loans held-for-sale	215,231	332,485	370,570
Mortgage servicing rights	0	0	0
Nonqualified deferred compensation assets	7,783	7,222	6,545
Derivative assets	51,529	48,221	52,436
Total	2,162,098	2,506,166	2,244,624
Derivative liabilities	37,797	37,264	54,745
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	340,178	336,095	217,645
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	828,275	895,688	973,715
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	135,528	116,330	77,935
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	135,067	135,038	148,873
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	417,303	605,225	368,282
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	30,136	29,365	27,587
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	0	0	0
Mortgage loans held-for-sale	0	0	0
Mortgage servicing rights		8,946	7,344
Nonqualified deferred compensation assets	0	0	0
Derivative assets	0	0	0
Total	71,929	67,495	64,138
Derivative liabilities	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | US Treasury Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		36,386	32,324
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities		$ 22,163	$ 24,470