Securities (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	$ 820,728	$ 761,138
Available-for-sale, Unrealized Gains	7,525	20,808
Available-for-sale, Unrealized Losses	(19,776)	(896)
Available-for-sale, Fair Value	808,477	781,050
Obligations of states and political subdivisions [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	30,143	31,112
Available-for-sale, Unrealized Gains	1,075	1,928
Available-for-sale, Unrealized Losses	(11)	0
Available-for-sale, Fair Value	31,207	33,040
Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	397,409	345,528
Available-for-sale, Unrealized Gains	5,528	12,699
Available-for-sale, Unrealized Losses	(7,034)	(79)
Available-for-sale, Fair Value	395,903	358,148
Collateralized mortgage obligations issued or guaranteed by U.S. government sponsored enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	385,847	375,627
Available-for-sale, Unrealized Gains	912	6,181
Available-for-sale, Unrealized Losses	(12,324)	(120)
Available-for-sale, Fair Value	374,435	381,688
Private issue collateralized mortgage obligations [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	7,329	8,871
Available-for-sale, Unrealized Gains	10
Available-for-sale, Unrealized Losses	(407)	(697)
Available-for-sale, Fair Value	$ 6,932	$ 8,174