Investment Securities - Amortized cost and fair value of other investment securities - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Information with respect to sales of available-for-sale securities
Proceeds from Sale of Available-for-sale Securities	$ 210,943	$ 137
Amortized Cost
Due in one year or less	11,395
Due after one year through five years	130,863
Due after five years through ten years	253,665
Due after ten years	982,735
Total	1,378,658	962,067	$ 1,002,166
Fair Value
Due in one year or less	11,467
Due after one year through five years	131,582
Due after five years through ten years	255,714
Due after ten years	982,250
Fair Value	1,381,013	978,047	999,405
Amortized Cost
Due in one year or less	3,379
Due after one year through five years	1,928
Due after five years through ten years	788
Total	6,095	7,920	6,094
Fair Value
Due in one year or less	3,423
Due after one year through five years	1,996
Due after five years through ten years	798
Fair Value	6,217	8,280	6,250
Amortized Cost	13,501	9,539	9,482
Fair Value	13,501	9,539	9,482
Federal Home Loan Bank stock
Fair Value
Amortized Cost	11,239	7,897	7,840
Fair Value	11,239	7,897	7,840
Investment in unconsolidated subsidiaries
Fair Value
Amortized Cost	2,262	1,642	1,642
Fair Value	$ 2,262	$ 1,642	$ 1,642