Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)		Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure		$ 6,854,000	$ 9,181,000
U.S. government and federal agency obligations		826,494,000	851,776,000
Government-sponsored enterprise obligations		109,883,000	139,277,000
State and municipal obligations		1,448,952,000	1,267,927,000
Agency mortgage-backed securities		5,382,187,000	3,937,964,000
Non-agency mortgage-backed securities		600,196,000	809,782,000
Other asset-backed securities		1,448,225,000	1,233,489,000
Other debt securities		501,490,000	331,411,000
Trading securities		28,813,000	28,161,000
Equity securities with a readily determinable fair value		2,711,000	2,929,000
Private equity investments		73,846,000	94,122,000
Derivative Assets	[1]	269,010,000	105,674,000
Assets held in trust for deferred compensation plan		16,310,000	16,518,000
Assets, Fair Value Disclosure		10,714,971,000	8,828,211,000
Derivative Liabilities	[1]	21,373,000	10,219,000
Liabilities held in trust for deferred compensation plan		16,310,000	16,518,000
Total Liabilities		37,683,000	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		826,494,000	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		2,711,000	2,929,000
Private equity investments		0	0
Derivative Assets	[1]	0	0
Assets held in trust for deferred compensation plan		16,310,000	16,518,000
Assets, Fair Value Disclosure		845,515,000	871,223,000
Derivative Liabilities	[1]	0	0
Liabilities held in trust for deferred compensation plan		16,310,000	16,518,000
Total Liabilities		16,310,000	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		6,854,000	9,181,000
U.S. government and federal agency obligations		0	0
Government-sponsored enterprise obligations		109,883,000	139,277,000
State and municipal obligations		1,439,462,000	1,258,074,000
Agency mortgage-backed securities		5,382,187,000	3,937,964,000
Non-agency mortgage-backed securities		600,196,000	809,782,000
Other asset-backed securities		1,448,225,000	1,233,489,000
Other debt securities		501,490,000	331,411,000
Trading securities		28,813,000	28,161,000
Equity securities with a readily determinable fair value		0	0
Private equity investments		0	0
Derivative Assets	[1]	266,028,000	105,075,000
Assets held in trust for deferred compensation plan		0	0
Assets, Fair Value Disclosure		9,783,138,000	7,852,414,000
Derivative Liabilities	[1]	20,279,000	9,989,000
Liabilities held in trust for deferred compensation plan		0	0
Total Liabilities		20,279,000	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		9,490,000	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		73,846,000	94,122,000
Derivative Assets	[1]	2,982,000	599,000
Assets held in trust for deferred compensation plan		0	0
Assets, Fair Value Disclosure		86,318,000	104,574,000
Derivative Liabilities	[1]	1,094,000	230,000
Liabilities held in trust for deferred compensation plan		0	0
Total Liabilities		$ 1,094,000	$ 230,000

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