Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 13,595		$ 17,853
Private equity investments	67,044
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	367,497		364,665
Government-sponsored enterprise obligations	380,190		315,698
State and municipal obligations	1,461,251		1,245,284
Agency mortgage-backed securities	3,471,262		4,106,059
Non-agency mortgage-backed securities	255,172		316,902
Other asset-backed securities	2,930,810		2,693,143
Other debt securities	121,623		141,260
Equity securities	33,146		41,691
Trading securities	13,595		17,853
Private equity investments	67,044		66,978
Derivative Assets	18,863	[1]	21,537	[1]
Assets held in trust	5,404		4,506
Total Assets	9,125,857		9,335,576
Derivative Liabilities	19,867	[1]	22,722	[1]
Total Liabilities	19,867		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	367,497		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	19,253		27,808
Trading securities	0		0
Private equity investments	0		0
Derivative Assets	0	[1]	0	[1]
Assets held in trust	5,404		4,506
Total Assets	392,154		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	0		7,510
Government-sponsored enterprise obligations	380,190		315,698
State and municipal obligations	1,333,520		1,109,663
Agency mortgage-backed securities	3,471,262		4,106,059
Non-agency mortgage-backed securities	255,172		316,902
Other asset-backed securities	2,930,810		2,693,143
Other debt securities	121,623		141,260
Equity securities	13,893		13,883
Trading securities	13,595		17,853
Private equity investments	0		0
Derivative Assets	18,853	[1]	21,502	[1]
Assets held in trust	0		0
Total Assets	8,538,918		8,743,473
Derivative Liabilities	19,691	[1]	22,564	[1]
Total Liabilities	19,691		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	127,731		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	67,044		66,978
Derivative Assets	10	[1]	35	[1]
Assets held in trust	0		0
Total Assets	194,785		202,634
Derivative Liabilities	176	[1]	158	[1]
Total Liabilities	$ 176		$ 158

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