Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Investment Securities, Available-for-Sale, Amortized Cost
Due in one year or less	$ 4,567
Due after one year through five years	85,288
Due after five years through ten years	262,556
Due after ten years	1,170,460
Total	1,522,871	1,500,516
Investment Securities, Available-for-Sale, Estimated Fair Value
Due in one year or less	4,596
Due after one year through five years	85,219
Due after five years through ten years	268,665
Due after ten years	1,208,697
Available-for-sale, at fair value	$ 1,567,177	$ 1,494,745