Fair Value Measurements (Summary Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 34,178		$ 17,853
Derivatives, assets	18,785		21,537
Derivatives, liabilities	20,076		22,722
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	361,150		357,155
Equity securities	32,225		27,808
Assets held in trust	5,375		4,506
Total assets	398,750		389,469
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	7,512		7,510
Government-sponsored enterprise obligations	277,924		315,698
State and municipal obligations	1,196,994		1,109,663
Agency mortgage-backed securities	3,866,456		4,106,059
Non-agency mortgage-backed securities	294,221		316,902
Other asset-backed securities	2,817,492		2,693,143
Other debt securities	123,355		141,260
Equity securities	13,197		13,883
Trading securities	34,178		17,853
Derivatives, assets	18,776	[1]	21,502	[1]
Total assets	8,650,105		8,743,473
Derivatives, liabilities	19,961	[1]	22,564	[1]
Total liabilities	19,961		22,564
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
State and municipal obligations	129,873		135,621
Private equity investments	72,121		66,978
Derivatives, assets	9	[1]	35	[1]
Total assets	202,003		202,634
Derivatives, liabilities	115	[1]	158	[1]
Total liabilities	115		158
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	368,662		364,665
Government-sponsored enterprise obligations	277,924		315,698
State and municipal obligations	1,326,867		1,245,284
Agency mortgage-backed securities	3,866,456		4,106,059
Non-agency mortgage-backed securities	294,221		316,902
Other asset-backed securities	2,817,492		2,693,143
Other debt securities	123,355		141,260
Equity securities	45,422		41,691
Trading securities	34,178		17,853
Private equity investments	72,121		66,978
Derivatives, assets	18,785	[1]	21,537	[1]
Assets held in trust	5,375		4,506
Total assets	9,250,858		9,335,576
Derivatives, liabilities	20,076	[1]	22,722	[1]
Total liabilities	$ 20,076		$ 22,722

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