Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 15,327	$ 9,263
U.S. government and federal agency obligations	917,147	920,904
Government-sponsored enterprise obligations	406,363	449,998
State and municipal obligations	1,611,366	1,778,214
Agency mortgage-backed securities	3,040,913	2,685,931
Non-agency mortgage-backed securities	905,793	1,055,639
Asset-backed securities	1,492,800	2,381,301
Other debt securities	351,060	325,953
Equity securities	48,838	51,263
Trading securities	18,269	22,225
Private equity investments	55,752	50,820
Derivative Assets	8,349	13,566
Deferred Compensation Plan Assets	12,843	10,261
Total assets	8,884,820	9,755,338
Derivative Liability	8,074	13,339
Deferred Compensation Liability, Current and Noncurrent	12,843	10,261
Total liabilities	20,917	23,600
Quoted Prices In Active Markets For Identical Assets (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	917,147	920,904
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
Asset-backed securities	0	0
Other debt securities	0	0
Equity securities	19,864	24,967
Trading securities	0	0
Private equity investments	0	0
Derivative Assets	0	0
Deferred Compensation Plan Assets	12,843	10,261
Total assets	949,854	956,132
Derivative Liability	0	0
Deferred Compensation Liability, Current and Noncurrent	12,843	10,261
Total liabilities	12,843	10,261
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	15,327	9,263
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	406,363	449,998
State and municipal obligations	1,594,350	1,761,532
Agency mortgage-backed securities	3,040,913	2,685,931
Non-agency mortgage-backed securities	905,793	1,055,639
Asset-backed securities	1,492,800	2,381,301
Other debt securities	351,060	325,953
Equity securities	28,974	26,296
Trading securities	18,269	22,225
Private equity investments	0	0
Derivative Assets	7,723	13,146
Deferred Compensation Plan Assets	0	0
Total assets	7,861,572	8,731,284
Derivative Liability	7,951	13,177
Deferred Compensation Liability, Current and Noncurrent	0	0
Total liabilities	7,951	13,177
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	17,016	16,682
Agency mortgage-backed securities	0	0
Non-agency mortgage-backed securities	0	0
Asset-backed securities	0	0
Other debt securities	0	0
Equity securities	0	0
Trading securities	0	0
Private equity investments	55,752	50,820
Derivative Assets	626	420
Deferred Compensation Plan Assets	0	0
Total assets	73,394	67,922
Derivative Liability	123	162
Deferred Compensation Liability, Current and Noncurrent	0	0
Total liabilities	$ 123	$ 162