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	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	$ 637,663	$ 1,716,388	$ 2,162,061
Trading account securities	3,613	448	1,597
Mortgage loans held-for-sale	554,256	388,038	497,283
Derivative assets	89,036	42,779	36,747
Derivative liabilities	90,892	42,458	36,605
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	122,330	306,729	281,161
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	69,916	70,236	628,660
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	111,640	108,595	269,790
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	207,508	1,092,597	800,101
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	56,579	56,686	54,208
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	3,613	448	1,597
Mortgage loans held-for-sale	554,256	388,038	497,283
MSRs	13,382	9,092	8,034
Nonqualified deferred compensation assets	9,076	8,517	8,778
Derivative assets	101,052	51,298	48,918
Total	1,319,042	2,173,781	2,726,671
Derivative liabilities	100,912	45,019	40,500
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	122,330	306,729	281,161
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	69,916	70,236	628,660
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	111,640	108,595	269,790
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	69,690	81,545	128,141
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	207,508	1,092,597	800,101
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	56,579	56,686	54,208
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	3,613	448	1,597
Mortgage loans held-for-sale	554,256	388,038	497,283
MSRs	0	0	0
Nonqualified deferred compensation assets	9,076	8,517	8,778
Derivative assets	101,052	51,298	48,918
Total	1,210,661	2,070,877	2,635,069
Derivative liabilities	100,912	45,019	40,500
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	122,330	306,729	281,161
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	69,916	70,236	628,660
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	41,828	39,982	211,218
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	69,690	81,545	128,141
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	207,508	1,092,597	800,101
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	31,392	31,487	29,212
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
MSRs	13,382	9,092	8,034
Nonqualified deferred compensation assets	0	0	0
Derivative assets	0	0	0
Total	108,381	102,904	91,602
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	69,812	68,613	58,572
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	$ 25,187	$ 25,199	$ 24,996