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, 2015	Dec. 31, 2014	Jun. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	$ 2,162,061	$ 1,792,078	$ 1,824,240
Trading account securities	1,597	1,206	2,234
Mortgage loans held-for-sale, at fair value	497,283	351,290	363,627
Derivative assets	36,747	37,841	37,461
Derivative liabilities	36,605	36,921	36,733
U.S. Treasury
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	281,161	381,805	388,415
U.S. Government agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	628,660	668,316	766,000
Municipal
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	269,790	238,529	176,107
Mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	800,101	318,710	303,563
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, at fair value	54,208	51,139	54,852
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,597	1,206	2,234
Mortgage loans held-for-sale, at fair value	497,283	351,290	363,627
Mortgage servicing rights	8,034	8,435	8,227
Nonqualified deferred compensation assets	8,778	7,951	7,850
Derivative assets	48,918	47,964	50,967
Total	2,726,671	2,208,924	2,257,145
Derivative liabilities	40,500	41,180	43,650
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	281,161	381,805	388,415
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	628,660	668,316	766,000
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	269,790	238,529	176,107
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	128,141	133,579	135,303
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	800,101	318,710	303,563
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	54,208	51,139	54,852
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account securities	1,597	1,206	2,234
Mortgage loans held-for-sale, at fair value	497,283	351,290	363,627
Mortgage servicing rights	0	0	0
Nonqualified deferred compensation assets	8,778	7,951	7,850
Derivative assets	48,918	47,964	50,967
Total	2,635,069	2,117,825	2,186,713
Derivative liabilities	40,500	41,180	43,650
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	281,161	381,805	388,415
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	628,660	668,316	766,000
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	211,218	179,576	138,054
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	128,141	133,579	135,303
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	800,101	318,710	303,563
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	29,212	27,428	30,700
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, at fair value	0	0	0
Mortgage servicing rights	8,034	8,435	8,227
Nonqualified deferred compensation assets	0	0	0
Derivative assets	0	0	0
Total	91,602	91,099	70,432
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	58,572	58,953	38,053
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	$ 24,996	$ 23,711	$ 24,152