Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Investment Securities, Available-for-Sale, Amortized Cost
Due in one year or less	$ 2,803
Due after one year through five years	58,523
Due after five years through ten years	264,647
Due after ten years	1,191,452
Total	1,517,425	1,500,516
Investment Securities, Available-for-Sale, Estimated Fair Value
Due in one year or less	2,804
Due after one year through five years	58,864
Due after five years through ten years	268,537
Due after ten years	1,221,910
Available-for-sale, at fair value	$ 1,552,115	$ 1,494,745