Investment Securities - Amortized cost and fair value of other investment securities - (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 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	9,110
Due after one year through five years	114,456
Due after five years through ten years	160,581
Due after ten years	684,852
Total	968,999	$ 1,005,359	$ 835,778
Fair Value
Due in one year or less	9,207
Due after one year through five years	115,614
Due after five years through ten years	165,836
Due after ten years	698,953
Fair Value	989,610	1,009,541	841,661
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	3,009
Total	7,921	9,314	9,659
Fair Value
Due in one year or less	1,988
Due after one year through five years	3,127
Due after five years through ten years	3,116
Fair Value	8,231	9,723	10,114
Amortized Cost	9,529	8,893	9,031
Fair Value	9,529	8,893	9,031
Federal Home Loan Bank stock
Fair Value
Amortized Cost	7,887	7,251	7,389
Fair Value	7,887	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