Securities (Amortized Cost and Estimated Fair Values of Debt Securities by Contractual Maturity) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Available-for-sale, Amortized Cost
Due in one year or less	$ 3,395
Due after one year through five years	21,520
Due after five years through ten years	141,215
Due after ten years	595,008
Total	761,138
Available-for-sale, Fair Value
Due in one year or less	3,438
Due after one year through five years	22,342
Due after five years through ten years	146,362
Due after ten years	608,908
Total	$ 781,050