Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 11,320,000	$ 9,263,000
U.S. government and federal agency obligations	918,604,000	920,904,000
Government-sponsored enterprise obligations	469,414,000	449,998,000
State and municipal obligations	1,720,403,000	1,778,214,000
Agency mortgage-backed securities	2,756,973,000	2,685,931,000
Non-agency mortgage-backed securities	1,066,764,000	1,055,639,000
Other asset-backed securities	1,736,966,000	2,381,301,000
Other debt securities	356,641,000	325,953,000
Equity securities	83,522,000	51,263,000
Trading securities	24,605,000	22,225,000
Private equity investments	50,254,000	50,820,000
Derivative Assets	11,650,000	13,566,000
Assets held in trust for deferred compensation plan	12,311,000	10,261,000
Total Assets	9,219,427,000	9,755,338,000
Derivative Liabilities	5,979,000	13,339,000
Liabilities held in trust for deferred compensation plan	12,311,000	10,261,000
Total Liabilities	18,290,000	23,600,000
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	918,604,000	920,904,000
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
Equity securities	32,915,000	24,967,000
Trading securities	0	0
Private equity investments	0	0
Derivative Assets	0	0
Assets held in trust for deferred compensation plan	12,311,000	10,261,000
Total Assets	963,830,000	956,132,000
Derivative Liabilities	0	0
Liabilities held in trust for deferred compensation plan	12,311,000	10,261,000
Total Liabilities	12,311,000	10,261,000
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	11,320,000	9,263,000
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	469,414,000	449,998,000
State and municipal obligations	1,703,550,000	1,761,532,000
Agency mortgage-backed securities	2,756,973,000	2,685,931,000
Non-agency mortgage-backed securities	1,066,764,000	1,055,639,000
Other asset-backed securities	1,736,966,000	2,381,301,000
Other debt securities	356,641,000	325,953,000
Equity securities	50,607,000	26,296,000
Trading securities	24,605,000	22,225,000
Private equity investments	0	0
Derivative Assets	10,837,000	13,146,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	8,187,677,000	8,731,284,000
Derivative Liabilities	5,850,000	13,177,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	5,850,000	13,177,000
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	16,853,000	16,682,000
Agency mortgage-backed securities	0	0
Non-agency mortgage-backed securities	0	0
Other asset-backed securities	0	0
Other debt securities	0	0
Equity securities	0	0
Trading securities	0	0
Private equity investments	50,254,000	50,820,000
Derivative Assets	813,000	420,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	67,920,000	67,922,000
Derivative Liabilities	129,000	162,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	$ 129,000	$ 162,000