Investment Securities - Amortized cost and fair value of other investment securities - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2015
Information with respect to sales of Held to Maturity
Proceeds from Sale of Held-to-maturity Securities		$ 411
Gross realized losses		(90)
Net realized loss		(90)
Information with respect to sales of available-for-sale securities
Proceeds from Sale of Available-for-sale Securities	$ 137	9,315
Gross realized gains	122	115
Gross realized losses		(27)
Net realized gain	122	$ 88
Amortized Cost
Due in one year or less	6,649
Due after one year through five years	96,314
Due after five years through ten years	188,353
Due after ten years	710,850
Total	1,002,166		$ 1,005,359
Fair Value
Due in one year or less	6,709
Due after one year through five years	96,314
Due after five years through ten years	190,011
Due after ten years	706,371
Fair Value	999,405		1,009,541
Amortized Cost
Due in one year or less	2,779
Due after one year through five years	1,872
Due after five years through ten years	1,443
Total	6,094		9,314
Fair Value
Due in one year or less	2,826
Due after one year through five years	1,946
Due after five years through ten years	1,478
Fair Value	6,250		9,723
Amortized Cost	9,482		8,893
Fair Value	9,482		8,893
Federal Home Loan Bank stock
Fair Value
Amortized Cost	7,840		7,251
Fair Value	7,840		7,251
Investment in unconsolidated subsidiaries
Fair Value
Amortized Cost	1,642		1,642
Fair Value	$ 1,642		$ 1,642