Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	$ 803,271	$ 811,369
Unrealized Gains	(5,834)	(13,097)
Unrealized Losses	(23,412)	(9,535)
Securities available-for-sale	785,693	814,931
US Government Agencies Debt Securities [Member]
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	13,042	13,989
Unrealized Gains	(2)	(24)
Unrealized Losses	(571)	(318)
Securities available-for-sale	12,473	13,695
Mortgage Backed Securities - Residential
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	189,999	215,079
Unrealized Gains	(798)	(2,071)
Unrealized Losses	(6,146)	(1,812)
Securities available-for-sale	184,651	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	368,486	346,005
Unrealized Gains	(26)	(370)
Unrealized Losses	(13,965)	(6,705)
Securities available-for-sale	354,547	339,670
State and Municipal Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	231,565	227,651
Unrealized Gains	(1,764)	(4,671)
Unrealized Losses	(2,730)	(700)
Securities available-for-sale	230,599	231,622
Collateralized Debt Obligations
Amortized cost and fair value of investments classified as available for sale
Amortized Cost	179	8,644
Unrealized Gains	(3,244)	(5,961)
Unrealized Losses	0	0
Securities available-for-sale	$ 3,423	$ 14,605