Investment Securities - Amortized cost and fair value of other investment securities - (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Information with respect to sales of available-for-sale securities
Proceeds from Sale of Available-for-sale Securities	$ 215,987	$ 137
Amortized Cost
Due in one year or less	13,005
Due after one year through five years	110,358
Due after five years through ten years	272,409
Due after ten years	941,832
Total	1,337,604	968,999	$ 1,002,166
Fair Value
Due in one year or less	13,107
Due after one year through five years	110,976
Due after five years through ten years	274,466
Due after ten years	943,103
Fair Value	1,341,652	989,610	999,405
Amortized Cost
Due in one year or less	2,226
Due after one year through five years	1,152
Due after five years through ten years	788
Total	4,166	7,921	6,094
Fair Value
Due in one year or less	2,269
Due after one year through five years	1,186
Due after five years through ten years	793
Fair Value	4,248	8,231	6,250
Amortized Cost	13,076	9,529	9,482
Fair Value	13,076	9,529	9,482
Federal Home Loan Bank stock
Fair Value
Amortized Cost	10,814	7,887	7,840
Fair Value	10,814	7,887	7,840
Investment in unconsolidated subsidiaries
Fair Value
Amortized Cost	2,262	1,642	1,642
Fair Value	$ 2,262	$ 1,642	$ 1,642