Securities (Unrealized Gross Losses and Estimated Fair values of Investment Securities by Length of Time that Individual Securities in Each Category in Continuous Loss Position) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	$ 120,364	$ 386,967
Unrealized Losses - Less Than 12 Months	(611)	(11,942)
Fair Value - 12 Months or More	307,951	122,236
Unrealized Losses - 12 Months or More	(7,313)	(7,834)
Fair Value	428,315	509,203
Unrealized Losses	(7,924)	(19,776)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	5,756
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	5,756
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	19
Obligations of U.S. government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	42,856	145,424
Unrealized Losses - Less Than 12 Months	(171)	(4,189)
Fair Value - 12 Months or More	125,439	43,915
Unrealized Losses - 12 Months or More	(1,834)	(2,845)
Fair Value	168,295	189,339
Unrealized Losses	(2,005)	(7,034)
Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	75,723	239,278
Unrealized Losses - Less Than 12 Months	(432)	(7,738)
Fair Value - 12 Months or More	182,512	73,376
Unrealized Losses - 12 Months or More	(5,479)	(4,586)
Fair Value	258,235	312,654
Unrealized Losses	(5,911)	(12,324)
Private issue collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months	1,785	122
Unrealized Losses - Less Than 12 Months	(8)	(4)
Fair Value - 12 Months or More	0	4,945
Unrealized Losses - 12 Months or More	0	(403)
Fair Value	1,785	5,067
Unrealized Losses	(8)	(407)
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value - Less Than 12 Months		2,143
Unrealized Losses - Less Than 12 Months		(11)
Fair Value - 12 Months or More		0
Unrealized Losses - 12 Months or More		0
Fair Value		2,143
Unrealized Losses		(11)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	5,756
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	(19)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	5,756
Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 19