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, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading securities	$ 23,400	$ 28,837
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
U.S. government and federal agency obligations	437,308	438,759
Government-sponsored enterprise obligations	453,702	471,574
State and municipal obligations	1,659,168	1,615,707
Agency mortgage-backed securities	3,268,377	3,380,955
Non-agency mortgage-backed securities	243,907	237,011
Other asset-backed securities	3,285,310	3,167,394
Other debt securities	172,019	177,752
Equity securities	52,960	33,096
Trading securities	23,400	28,837
Private equity investments	68,103	68,167
Derivative Assets	16,145	16,740
Assets held in trust	6,531	5,440
Total Assets	9,686,930	9,641,432
Derivative Liabilities	16,794	17,718
Total Liabilities	16,794	17,718
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	437,308	438,759
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	34,563	17,835
Trading securities	0	0
Private equity investments	0	0
Derivative Assets	0	0
Assets held in trust	6,531	5,440
Total Assets	478,402	462,034
Derivative Liabilities	0	0
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	0
Government-sponsored enterprise obligations	453,702	471,574
State and municipal obligations	1,531,025	1,489,293
Agency mortgage-backed securities	3,268,377	3,380,955
Non-agency mortgage-backed securities	243,907	237,011
Other asset-backed securities	3,285,310	3,167,394
Other debt securities	172,019	177,752
Equity securities	18,397	15,261
Trading securities	23,400	28,837
Private equity investments	0	0
Derivative Assets	16,137	16,731
Assets held in trust	0	0
Total Assets	9,012,274	8,984,808
Derivative Liabilities	16,655	17,522
Total Liabilities	16,655	17,522
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	128,143	126,414
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	68,103	68,167
Derivative Assets	8	9
Assets held in trust	0	0
Total Assets	196,254	194,590
Derivative Liabilities	139	196
Total Liabilities	$ 139	$ 196