Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 9,285,000	$ 13,529,000
U.S. government and federal agency obligations	845,939,000	907,652,000
Government-sponsored enterprise obligations	200,137,000	195,778,000
State and municipal obligations	1,237,456,000	1,328,039,000
Agency mortgage-backed securities	3,729,632,000	3,214,985,000
Non-agency mortgage-backed securities	1,010,667,000	1,047,716,000
Other asset-backed securities	1,326,178,000	1,511,614,000
Other debt securities	332,294,000	332,257,000
Trading securities	36,508,000	27,059,000
Equity securities with a readily determinable fair value	2,847,000	2,585,000
Private equity investments	86,411,000	85,659,000
Derivative Assets	106,430,000	41,210,000
Assets held in trust for deferred compensation plan	15,445,000	12,968,000
Assets, Fair Value Disclosure	8,939,229,000	8,721,051,000
Derivative Liabilities	10,012,000	13,421,000
Liabilities held in trust for deferred compensation plan	15,445,000	12,968,000
Total Liabilities	25,457,000	26,389,000
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	845,939,000	907,652,000
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 with a readily determinable fair value	2,847,000	2,585,000
Private equity investments	0	0
Derivative Assets	0	0
Assets held in trust for deferred compensation plan	15,445,000	12,968,000
Assets, Fair Value Disclosure	864,231,000	923,205,000
Derivative Liabilities	0	0
Liabilities held in trust for deferred compensation plan	15,445,000	12,968,000
Total Liabilities	15,445,000	12,968,000
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	9,285,000	13,529,000
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	200,137,000	195,778,000
State and municipal obligations	1,225,815,000	1,313,881,000
Agency mortgage-backed securities	3,729,632,000	3,214,985,000
Non-agency mortgage-backed securities	1,010,667,000	1,047,716,000
Other asset-backed securities	1,326,178,000	1,511,614,000
Other debt securities	332,294,000	332,257,000
Trading securities	36,508,000	27,059,000
Equity securities with a readily determinable fair value	0	0
Private equity investments	0	0
Derivative Assets	105,321,000	40,627,000
Assets held in trust for deferred compensation plan	0	0
Assets, Fair Value Disclosure	7,975,837,000	7,697,446,000
Derivative Liabilities	9,786,000	13,328,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	9,786,000	13,328,000
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	11,641,000	14,158,000
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 with a readily determinable fair value	0	0
Private equity investments	86,411,000	85,659,000
Derivative Assets	1,109,000	583,000
Assets held in trust for deferred compensation plan	0	0
Assets, Fair Value Disclosure	99,161,000	100,400,000
Derivative Liabilities	226,000	93,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	$ 226,000	$ 93,000