Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgages Held-for-sale, Fair Value Disclosure	$ 4,447,000	$ 4,981,000
U.S. government and federal agency obligations	755,649,000	727,076,000
Government-sponsored enterprise obligations	451,242,000	793,023,000
State and municipal obligations	1,836,001,000	1,741,957,000
Agency mortgage-backed securities	2,663,677,000	2,618,281,000
Non-agency mortgage-backed securities	937,208,000	879,963,000
Other asset-backed securities	2,409,324,000	2,644,381,000
Other debt securities	338,812,000	331,320,000
Equity securities	46,958,000	41,003,000
Trading securities	28,586,000	11,890,000
Private equity investments	59,486,000	63,032,000
Derivative Assets	32,056,000	12,771,000
Assets held in trust for deferred compensation plan	10,028,000	9,278,000
Total Assets	9,573,474,000	9,878,956,000
Derivative Liabilities	31,772,000	12,729,000
Liabilities held in trust for deferred compensation plan	10,028,000	9,278,000
Total Liabilities	41,800,000	22,007,000
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	755,649,000	727,076,000
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	23,045,000	20,263,000
Trading securities	0	0
Private equity investments	0	0
Derivative Assets	0	0
Assets held in trust for deferred compensation plan	10,028,000	9,278,000
Total Assets	788,722,000	756,617,000
Derivative Liabilities	0	0
Liabilities held in trust for deferred compensation plan	10,028,000	9,278,000
Total Liabilities	10,028,000	9,278,000
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	4,447,000	4,981,000
U.S. government and federal agency obligations	0	0
Government-sponsored enterprise obligations	451,242,000	793,023,000
State and municipal obligations	1,819,093,000	1,724,762,000
Agency mortgage-backed securities	2,663,677,000	2,618,281,000
Non-agency mortgage-backed securities	937,208,000	879,963,000
Other asset-backed securities	2,409,324,000	2,644,381,000
Other debt securities	338,812,000	331,320,000
Equity securities	23,913,000	20,740,000
Trading securities	28,586,000	11,890,000
Private equity investments	0	0
Derivative Assets	31,179,000	12,507,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	8,707,481,000	9,041,848,000
Derivative Liabilities	31,500,000	12,534,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	31,500,000	12,534,000
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	16,908,000	17,195,000
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	59,486,000	63,032,000
Derivative Assets	877,000	264,000
Assets held in trust for deferred compensation plan	0	0
Total Assets	77,271,000	80,491,000
Derivative Liabilities	272,000	195,000
Liabilities held in trust for deferred compensation plan	0	0
Total Liabilities	$ 272,000	$ 195,000