Investment Securities - Amortized cost and fair value of other investment securities - (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	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	9,315	$ 177,468
Gross realized gains	115
Gross realized losses	(27)
Net realized gain	88
Amortized Cost
Due in one year or less			$ 8,531
Due after one year through five years			115,982
Due after five years through ten years			201,646
Due after ten years			679,200
Total	797,930		1,005,359
Fair Value
Due in one year or less			8,629
Due after one year through five years			116,072
Due after five years through ten years			204,456
Due after ten years			680,384
Fair Value	806,766		1,009,541
Amortized Cost
Due in one year or less			640
Due after one year through five years			1,832
Due after five years through ten years			6,842
Total	9,659		9,314
Fair Value
Due in one year or less			644
Due after one year through five years			1,922
Due after five years through ten years			7,157
Fair Value	10,233		9,723
Amortized Cost	10,518		8,893
Fair Value	10,518		8,893
Federal Home Loan Bank stock
Fair Value
Amortized Cost	7,484		7,251
Fair Value	7,484		7,251
Investment in unconsolidated subsidiaries
Fair Value
Amortized Cost	3,034		1,642
Fair Value	$ 3,034		$ 1,642