Investment Securities, Available-for-sale Securities, Maturities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015
Amortized Cost [Abstract]
Due in one year or less	$ 4,087
Due in one year through five years	523,915
Due after five years through ten years	141,890
Due after ten years	18
Amortized Cost	669,910
Fair Value [Abstract]
Due in one year or less	4,092
Due in one year through five years	522,927
Due after five years through ten years	139,779
Due after ten years	18
Fair Value	$ 666,816