Securities (Securities Available for Sale) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 984,075	$ 969,359
Gross Unrealized Gains	35,985	38,606
Gross Unrealized Losses	(7,898)	(6,300)
Fair Value	1,012,162	1,001,665
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	502,652	561,076
Gross Unrealized Gains	15,484	16,719
Gross Unrealized Losses	(6,181)	(5,426)
Fair Value	511,955	572,369
State and Municipal Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	256,608	265,070
Gross Unrealized Gains	19,586	20,893
Gross Unrealized Losses	(589)	(388)
Fair Value	275,605	285,575
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	201,680	120,085
Gross Unrealized Gains	828	851
Gross Unrealized Losses	(981)	(435)
Fair Value	201,527	120,501
US Treasury Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,811	19,804
Gross Unrealized Gains	0	39
Gross Unrealized Losses	(105)	(15)
Fair Value	19,706	19,828
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,324	3,324
Gross Unrealized Gains	87	104
Gross Unrealized Losses	(42)	(36)
Fair Value	$ 3,369	$ 3,392