Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 1,438,716	$ 1,442,724
Gross Unrealized Gains	6,051	6,233
Gross Unrealized Losses	17,244	19,419
Fair Value	1,427,523	1,429,538
Obligations of U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	527,190	527,057
Gross Unrealized Gains	2,756	2,873
Gross Unrealized Losses	1,971	2,303
Fair Value	527,975	527,627
Obligations of U.S. states and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	92,877	89,910
Gross Unrealized Gains	424	286
Gross Unrealized Losses	744	1,140
Fair Value	92,557	89,056
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	155,224	159,417
Gross Unrealized Gains	1,069	1,081
Gross Unrealized Losses	2,160	2,272
Fair Value	154,133	158,226
U.S. Government sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	659,819	662,724
Gross Unrealized Gains	1,802	1,993
Gross Unrealized Losses	11,948	13,287
Fair Value	649,673	651,430
Non-U.S. Government agencies or sponsored entities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	106	116
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	106	116
U.S. corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,500	2,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	338	338
Fair Value	2,162	2,162
Total debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,437,716	1,441,724
Gross Unrealized Gains	6,051	6,233
Gross Unrealized Losses	17,161	19,340
Fair Value	1,426,606	1,428,617
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,000	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	83	79
Fair Value	$ 917	$ 921