Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 6,480,000	$ 15,327,000
U.S. government and federal agency obligations	911,923,000	917,147,000
Government-sponsored enterprise obligations	388,599,000	406,363,000
State and municipal obligations	1,416,845,000	1,611,366,000
Agency mortgage-backed securities	2,954,994,000	3,040,913,000
Non-agency mortgage-backed securities	960,612,000	905,793,000
Other asset-backed securities	1,466,035,000	1,492,800,000
Other debt securities	333,172,000	351,060,000
Trading securities	32,025,000	18,269,000
Equity securities, FV-NI	49,784,000	48,838,000
Private equity investments	64,951,000	55,752,000
Derivative Assets	5,092,000	8,349,000
Assets held in trust for deferred compensation plan	13,582,000	12,843,000
Total Assets	8,604,094,000	8,884,820,000
Derivative Liabilities	16,373,000	8,074,000
Liabilities held in trust for deferred compensation plan	13,582,000	12,843,000
Total Liabilities	29,955,000	20,917,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
U.S. government and federal agency obligations	911,923,000	917,147,000
Government-sponsored enterprise obligations	0	0
State and municipal obligations	0	0
Agency mortgage-backed securities	0	0
Non-agency mortgage-backed securities	0	0
Other asset-backed securities	0	0
Other debt securities	0	0
Trading securities	0	0
Equity securities, FV-NI	20,151,000	19,864,000
Private equity investments	0	0
Derivative Assets	0	0
Assets held in trust for deferred compensation plan	13,582,000	12,843,000
Total Assets	945,656,000	949,854,000
Derivative Liabilities	0	0
Liabilities held in trust for deferred compensation plan	13,582,000	12,843,000
Total Liabilities	13,582,000	12,843,000
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	6,480,000	15,327,000
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	388,599,000	406,363,000
State and municipal obligations	1,399,687,000	1,594,350,000
Agency mortgage-backed securities	2,954,994,000	3,040,913,000
Non-agency mortgage-backed securities	960,612,000	905,793,000
Other asset-backed securities	1,466,035,000	1,492,800,000
Other debt securities	333,172,000	351,060,000
Trading securities	32,025,000	18,269,000
Equity securities, FV-NI	29,633,000	28,974,000
Private equity investments	0	0
Derivative Assets	4,481,000	7,723,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	7,575,718,000	7,861,572,000
Derivative Liabilities	16,282,000	7,951,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	16,282,000	7,951,000
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	0	0
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	0	0
State and municipal obligations	17,158,000	17,016,000
Agency mortgage-backed securities	0	0
Non-agency mortgage-backed securities	0	0
Other asset-backed securities	0	0
Other debt securities	0	0
Trading securities	0	0
Equity securities, FV-NI	0	0
Private equity investments	64,951,000	55,752,000
Derivative Assets	611,000	626,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	82,720,000	73,394,000
Derivative Liabilities	91,000	123,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	$ 91,000	$ 123,000