Investment Securities - Amortized cost and fair value of other investment securities - (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Information with respect to sales of available-for-sale securities
Proceeds from Sale of Available-for-sale Securities	$ 137
Gain on sale of securities	122
Amortized Cost
Due in one year or less	6,804
Due after one year through five years	90,063
Due after five years through ten years	153,896
Due after ten years	658,387
Total	909,150	$ 1,005,359	$ 873,981
Fair Value
Due in one year or less	6,861
Due after one year through five years	90,966
Due after five years through ten years	158,477
Due after ten years	669,070
Fair Value	925,374	1,009,541	885,798
Amortized Cost
Due in one year or less	1,928
Due after one year through five years	2,984
Due after five years through ten years	1,939
Total	6,851	9,314	9,314
Fair Value
Due in one year or less	1,969
Due after one year through five years	3,084
Due after five years through ten years	2,023
Fair Value	7,076	9,723	9,758
Amortized Cost	9,482	8,893	9,031
Fair Value	9,482	8,893	9,031
Federal Home Loan Bank stock
Fair Value
Amortized Cost	7,840	7,251	7,389
Fair Value	7,840	7,251	7,389
Investment in unconsolidated subsidiaries
Fair Value
Amortized Cost	1,642	1,642	1,642
Fair Value	$ 1,642	$ 1,642	$ 1,642