Securities (Schedule of Amortized Cost and Fair Value of Securities Held to Maturity) (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 1,010,672	$ 940,481
Gross Unrealized Gains	31,213	26,682
Gross Unrealized Losses	(3,451)	(7,749)
Held to Maturity, Fair Value, total	1,038,434	959,414
U.S. Treasury and Other U.S. Government Agencies and Corporations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	4,666	4,925
Gross Unrealized Gains	229	212
Held to Maturity, Fair Value, total	4,895	5,137
Agency Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	758,325	688,575
Gross Unrealized Gains	26,724	23,878
Gross Unrealized Losses	(1,556)	(3,079)
Held to Maturity, Fair Value, total	783,493	709,374
Agency Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	62,673	71,102
Gross Unrealized Gains	609	511
Gross Unrealized Losses	(164)	(889)
Held to Maturity, Fair Value, total	63,118	70,724
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	28,347	33,950
Gross Unrealized Gains	243	328
Gross Unrealized Losses	(908)	(1,331)
Held to Maturity, Fair Value, total	27,682	32,947
States Of The U.S. And Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	152,574	137,210
Gross Unrealized Gains	3,383	1,735
Gross Unrealized Losses	(311)	(1,630)
Held to Maturity, Fair Value, total	155,646	137,315
Collateralized Debt Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,502	3,132
Gross Unrealized Losses	(508)	(778)
Held to Maturity, Fair Value, total	1,994	2,354
Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	1,585	1,587
Gross Unrealized Gains	25	18
Gross Unrealized Losses	(4)	(42)
Held to Maturity, Fair Value, total	$ 1,606	$ 1,563