Bank subsidiary (Details 6) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Amortized Cost
Due in one year or less	$ 68,120
Due after one year through five years	63,839
Due after five years through ten years	78,211
Due after ten years	32,955
Total amortized cost	243,125
Mortgage-related securities-FNMA, FHLMC and GNMA - amortized cost	399,784
Total available-for-sale securities, amortized cost	642,909	653,492
Fair value
Due in one year or less	68,635
Due after one year through five years	65,258
Due after five years through ten years	82,977
Due after ten years	33,191
Total fair value	250,061
Mortgage-related securities-FNMA, FHLMC and GNMA - fair value	409,339
Total available for sale securities	$ 659,400	$ 671,358