Securities, Held to Maturity (Details) $ in Thousands	Dec. 31, 2017 USD ($) Position	Dec. 31, 2016 USD ($) Position
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 484,073	$ 527,948
Unrealized gains	1,805	1,581
Unrealized losses	4,007	4,479
Estimated fair value	481,871	525,050
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	156,340	286,063
12 months or longer	87,037	35,209
Total	243,377	321,272
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,336)	(3,290)
12 months or longer	(2,671)	(1,189)
Total	$ (4,007)	$ (4,479)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	59	172
12 months or longer | Position	32	4
Total | Position	91	176
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Within one year	$ 31,412
From one to five years	42,363
From five to ten years	174,950
After ten years	235,348
Amortized cost	484,073	$ 527,948
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Within one year	31,413
From one to five years	42,588
From five to ten years	174,937
After ten years	232,933
Fair value	481,871	525,050
Mortgage-Backed [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	15,477	95,492
12 months or longer	33,703	0
Total	49,180	95,492
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(140)	(1,176)
12 months or longer	(670)	0
Total	$ (810)	$ (1,176)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	2	5
12 months or longer | Position	2	0
Total | Position	4	5
Mortgage-backed Securities, Issued by US Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 96,357	$ 96,668
Unrealized gains	85	0
Unrealized losses	810	1,176
Estimated fair value	95,632	95,492
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized cost	96,357	96,668
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Fair value	95,632	95,492
Mortgage-Backed, U.S. Government Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	418	533
Unrealized gains	57	87
Unrealized losses	0	0
Estimated fair value	475	620
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized cost	418	533
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Fair value	475	620
Collateralized Mortgage Obligations [Member]
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	118,476	108,587
12 months or longer	37,614	35,209
Total	156,090	143,796
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(1,064)	(319)
12 months or longer	(1,513)	(1,189)
Total	$ (2,577)	$ (1,508)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	17	12
12 months or longer | Position	6	4
Total | Position	23	16
Collateralized Mortgage Obligations, Government-Sponsored Enterprises [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	$ 186,327	$ 225,213
Unrealized gains	224	1,060
Unrealized losses	2,577	1,508
Estimated fair value	183,974	224,765
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized cost	186,327	225,213
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Fair value	183,974	224,765
State & Municipal [Member]
Schedule of Held-to-maturity Securities [Line Items]
Amortized cost	200,971	205,534
Unrealized gains	1,439	434
Unrealized losses	620	1,795
Estimated fair value	201,790	204,173
Unrealized Loss Position, Fair Value [Abstract]
Less than 12 months	22,387	81,984
12 months or longer	15,720	0
Total	38,107	81,984
Unrealized Loss Position, Unrealized Losses [Abstract]
Less than 12 months	(132)	(1,795)
12 months or longer	(488)	0
Total	$ (620)	$ (1,795)
Unrealized Loss Position, Number of Positions [Abstract]
Less than 12 months | Position	40	155
12 months or longer | Position	24	0
Total | Position	64	155
Held-to-maturity Securities, Debt Maturities, Amortized Cost [Abstract]
Amortized cost	$ 200,971	$ 205,534
Held-to-maturity Securities, Debt Maturities, Estimated Fair Value [Abstract]
Fair value	$ 201,790	$ 204,173