Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 14,313		$ 17,853
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	370,123		364,665
Government-sponsored enterprise obligations	266,702		315,698
State and municipal obligations	1,358,537		1,245,284
Agency mortgage-backed securities	3,802,110		4,106,059
Non-agency mortgage-backed securities	269,304		316,902
Other asset-backed securities	2,991,092		2,693,143
Other debt securities	110,814		141,260
Equity securities	37,769		41,691
Trading securities	14,313		17,853
Private equity investments	65,766		66,978
Derivative Assets	20,445	[1]	21,537	[1]
Assets held in trust	5,145		4,506
Total Assets	9,312,120		9,335,576
Derivative Liabilities	21,515	[1]	22,722	[1]
Total Liabilities	21,515		22,722
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	362,608		357,155
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	24,373		27,808
Trading securities	0		0
Private equity investments	0		0
Derivative Assets	0	[1]	0	[1]
Assets held in trust	5,145		4,506
Total Assets	392,126		389,469
Derivative Liabilities	0	[1]	0	[1]
Total Liabilities	0		0
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	7,515		7,510
Government-sponsored enterprise obligations	266,702		315,698
State and municipal obligations	1,230,997		1,109,663
Agency mortgage-backed securities	3,802,110		4,106,059
Non-agency mortgage-backed securities	269,304		316,902
Other asset-backed securities	2,991,092		2,693,143
Other debt securities	110,814		141,260
Equity securities	13,396		13,883
Trading securities	14,313		17,853
Private equity investments	0		0
Derivative Assets	20,435	[1]	21,502	[1]
Assets held in trust	0		0
Total Assets	8,726,678		8,743,473
Derivative Liabilities	21,406	[1]	22,564	[1]
Total Liabilities	21,406		22,564
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	0		0
Government-sponsored enterprise obligations	0		0
State and municipal obligations	127,540		135,621
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	65,766		66,978
Derivative Assets	10	[1]	35	[1]
Assets held in trust	0		0
Total Assets	193,316		202,634
Derivative Liabilities	109	[1]	158	[1]
Total Liabilities	$ 109		$ 158

[1] The fair value of each class of derivative is shown in Note 10