Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)		Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure		$ 108,000	$ 9,181,000
U.S. government and federal agency obligations		840,447,000	851,776,000
Government-sponsored enterprise obligations		112,870,000	139,277,000
State and municipal obligations		1,283,068,000	1,267,927,000
Agency mortgage-backed securities		4,168,421,000	3,937,964,000
Non-agency mortgage-backed securities		717,008,000	809,782,000
Other asset-backed securities		1,232,292,000	1,233,489,000
Other debt securities		324,480,000	331,411,000
Trading securities		24,291,000	28,161,000
Equity securities with a readily determinable fair value		2,633,000	2,929,000
Private equity investments		81,159,000	94,122,000
Derivative Assets	[1]	250,450,000	105,674,000
Assets held in trust for deferred compensation plan		14,194,000	16,518,000
Assets, Fair Value Disclosure		9,051,421,000	8,828,211,000
Derivative Liabilities	[1]	20,443,000	10,219,000
Liabilities held in trust for deferred compensation plan		14,194,000	16,518,000
Total Liabilities		34,637,000	26,737,000
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		840,447,000	851,776,000
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		2,633,000	2,929,000
Private equity investments		0	0
Derivative Assets	[1]	0	0
Assets held in trust for deferred compensation plan		14,194,000	16,518,000
Assets, Fair Value Disclosure		857,274,000	871,223,000
Derivative Liabilities	[1]	0	0
Liabilities held in trust for deferred compensation plan		14,194,000	16,518,000
Total Liabilities		14,194,000	16,518,000
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		108,000	9,181,000
U.S. government and federal agency obligations		0	0
Government-sponsored enterprise obligations		112,870,000	139,277,000
State and municipal obligations		1,274,706,000	1,258,074,000
Agency mortgage-backed securities		4,168,421,000	3,937,964,000
Non-agency mortgage-backed securities		717,008,000	809,782,000
Other asset-backed securities		1,232,292,000	1,233,489,000
Other debt securities		324,480,000	331,411,000
Trading securities		24,291,000	28,161,000
Equity securities with a readily determinable fair value		0	0
Private equity investments		0	0
Derivative Assets	[1]	250,026,000	105,075,000
Assets held in trust for deferred compensation plan		0	0
Assets, Fair Value Disclosure		8,104,202,000	7,852,414,000
Derivative Liabilities	[1]	19,462,000	9,989,000
Liabilities held in trust for deferred compensation plan		0	0
Total Liabilities		19,462,000	9,989,000
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		8,362,000	9,853,000
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		81,159,000	94,122,000
Derivative Assets	[1]	424,000	599,000
Assets held in trust for deferred compensation plan		0	0
Assets, Fair Value Disclosure		89,945,000	104,574,000
Derivative Liabilities	[1]	981,000	230,000
Liabilities held in trust for deferred compensation plan		0	0
Total Liabilities		$ 981,000	$ 230,000

[1] * The fair value of each class of derivative is shown in Note 11.