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	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	$ 770,983	$ 1,716,388	$ 1,721,030
Trading account securities	2,116	448	7,811
Mortgage loans held-for-sale	314,554	388,038	446,355
Derivative assets	73,985	42,779	47,550
Derivative liabilities	74,019	42,458	47,698
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	117,089	306,729	271,474
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	94,172	70,236	661,793
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	121,195	108,595	269,912
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	302,695	1,092,597	329,591
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	55,619	56,686	54,446
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	2,116	448	7,811
Mortgage loans held-for-sale	314,554	388,038	446,355
Mortgage servicing rights	10,128	9,092	7,852
Nonqualified deferred compensation assets	8,926	8,517	8,718
Derivative assets		51,298	62,984
Total	1,193,044	2,173,781	2,254,750
Derivative liabilities		45,019	55,225
Fair Value, Measurements, Recurring | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	117,089	306,729	271,474
Fair Value, Measurements, Recurring | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	94,172	70,236	661,793
Fair Value, Measurements, Recurring | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	121,195	108,595	269,912
Fair Value, Measurements, Recurring | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	80,213	81,545	133,814
Fair Value, Measurements, Recurring | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	302,695	1,092,597	329,591
Fair Value, Measurements, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	55,619	56,686	54,446
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	2,116	448	7,811
Mortgage loans held-for-sale	314,554	388,038	446,355
Mortgage servicing rights	0	0	0
Nonqualified deferred compensation assets	8,926	8,517	8,718
Derivative assets	86,337	51,298	62,984
Total	1,088,620	2,070,877	2,166,193
Derivative liabilities	81,712	45,019	55,225
Fair Value, Measurements, Recurring | Level 2 | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	117,089	306,729	271,474
Fair Value, Measurements, Recurring | Level 2 | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	94,172	70,236	661,793
Fair Value, Measurements, Recurring | Level 2 | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	50,953	39,982	213,863
Fair Value, Measurements, Recurring | Level 2 | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	80,213	81,545	133,814
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	302,695	1,092,597	329,591
Fair Value, Measurements, Recurring | Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	31,565	31,487	29,790
Fair Value, Measurements, Recurring | Level 3
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	10,128	9,092	7,852
Nonqualified deferred compensation assets	0	0	0
Derivative assets	0	0	0
Total	104,424	102,904	88,557
Derivative liabilities	0	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0	0	0
Fair Value, Measurements, Recurring | Level 3 | Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	70,242	68,613	56,049
Fair Value, Measurements, Recurring | Level 3 | Corporate notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0	0	0
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	0	0	0
Fair Value, Measurements, Recurring | Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	24,054	25,199	24,656
Other Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	86,337	51,298	62,984
Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	$ 81,712	$ 45,019	$ 55,225