Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	$ 795,380	$ 811,369
Unrealized Gains	(6,997)	(13,097)
Unrealized Losses	(19,768)	(9,535)
Securities available-for-sale	782,609	814,931
US Government Agencies Debt Securities [Member]
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	13,243	13,989
Unrealized Gains	(6)	(24)
Unrealized Losses	(472)	(318)
Securities available-for-sale	12,777	13,695
Mortgage Backed Securities - Residential
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	195,127	215,079
Unrealized Gains	(1,003)	(2,071)
Unrealized Losses	(5,391)	(1,812)
Securities available-for-sale	190,739	215,338
Mortgage Backed Securities - Commercial
Amortized cost and fair value of investments classified as available for sale
Amortized Cost		1
Unrealized Gains		0
Unrealized Losses		0
Securities available-for-sale		1
Collateralized Mortgage Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	356,689	346,005
Unrealized Gains	(54)	(370)
Unrealized Losses	(12,256)	(6,705)
Securities available-for-sale	344,487	339,670
State and Municipal Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	230,102	227,651
Unrealized Gains	(2,703)	(4,671)
Unrealized Losses	(1,649)	(700)
Securities available-for-sale	231,156	231,622
Collateralized Debt Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	219	8,644
Unrealized Gains	(3,231)	(5,961)
Unrealized Losses	0	0
Securities available-for-sale	$ 3,450	$ 14,605