Investment Securities Held to Maturity (Details) $ in Thousands	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 311,038	$ 301,876	$ 347,701
Equity Securities	1,579	0	0
Gross Unrealized Gains	354	935	1,519
Held-to-Maturity at Amortized Cost	330,124	335,907	335,211
Held-To-Maturity Securities, at Fair Value	324,938	335,901	335,105
Gross Unrealized Gains	646	1,960	2,708
Gross Unrealized Losses	5,832	1,966	2,813
Held-To-Maturity Securities, Pledged as Collateral	307,273	318,622	316,966
Maturities of Debt Securities, at Amortized Cost:
Within One Year	35,115
From 1 - 5 Years	132,555
From 5 - 10 Years	159,054
Over 10 Years	3,400
Maturities of Debt Securities, at Fair Value:
Within One Year	35,160
From 1 - 5 Years	132,124
From 5 - 10 Years	154,255
Over 10 Years	3,399
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	154,771	69,412	103,132
12 Months or Longer	68,269	68,409	657
Total	$ 223,040	$ 137,821	$ 103,789
Number of Securities in a Continuous Loss Position	542	366	259
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 2,748	$ 498	$ 2,810
12 Months or Longer	3,084	1,468	3
Total	5,832	1,966	2,813
State and Municipal Obligations
Schedule of Held-to-maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	9,741	10,351	25,467
Gross Unrealized Gains	7	9	40
Held-to-Maturity at Amortized Cost	272,938	275,530	263,642
Held-To-Maturity Securities, at Fair Value	268,605	275,353	263,255
Gross Unrealized Gains	646	1,691	2,410
Gross Unrealized Losses	4,979	1,868	2,796
Maturities of Debt Securities, at Amortized Cost:
Within One Year	35,115
From 1 - 5 Years	81,312
From 5 - 10 Years	153,111
Over 10 Years	3,400
Maturities of Debt Securities, at Fair Value:
Within One Year	35,160
From 1 - 5 Years	81,634
From 5 - 10 Years	148,412
Over 10 Years	3,399
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	101,695	55,648	95,450
12 Months or Longer	65,012	65,152	657
Total	$ 166,707	$ 120,800	$ 96,107
Number of Securities in a Continuous Loss Position	495	352	251
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 1,981	$ 442	$ 2,793
12 Months or Longer	2,998	1,425	3
Total	4,979	1,867	2,796
Mortgage-Backed Securities - Residential
Schedule of Held-to-maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	240,033	229,077	170,601
Gross Unrealized Gains	347	485	934
Held-to-Maturity at Amortized Cost	57,186	60,377	71,569
Held-To-Maturity Securities, at Fair Value	56,333	60,548	71,850
Gross Unrealized Gains	0	269	298
Gross Unrealized Losses	853	98	17
Maturities of Debt Securities, at Amortized Cost:
Within One Year	0
From 1 - 5 Years	51,243
From 5 - 10 Years	5,943
Over 10 Years	0
Maturities of Debt Securities, at Fair Value:
Within One Year	0
From 1 - 5 Years	50,490
From 5 - 10 Years	5,843
Over 10 Years	0
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	53,076	13,764	7,682
12 Months or Longer	3,257	3,257	0
Total	$ 56,333	$ 17,021	$ 7,682
Number of Securities in a Continuous Loss Position	47	14	8
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 767	$ 56	$ 17
12 Months or Longer	86	43	0
Total	853	99	17
Mortgage-Backed Securities - Residential | Agency Securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity at Amortized Cost	2,530	2,680	3,106
Mortgage-Backed Securities - Residential | US Government-sponsored Enterprises Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity at Amortized Cost	54,656	57,697	68,463
Corporate and Other Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,000	1,000	3,501
Gross Unrealized Gains	0	0	0
Held-to-Maturity at Amortized Cost	0	0	0
Held-To-Maturity Securities, at Fair Value	0	0	0
Gross Unrealized Gains	0	0	0
Gross Unrealized Losses	0	0	0
Maturities of Debt Securities, at Amortized Cost:
Within One Year	0
From 1 - 5 Years	0
From 5 - 10 Years	0
Over 10 Years	0
Maturities of Debt Securities, at Fair Value:
Within One Year	0
From 1 - 5 Years	0
From 5 - 10 Years	0
Over 10 Years	0
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	0	0	0
12 Months or Longer	0	0	0
Total	$ 0	$ 0	$ 0
Number of Securities in a Continuous Loss Position	0	0	0
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 0	$ 0	$ 0
12 Months or Longer	0	0	0
Total	0	0	0
Agency Securities | Mortgage-Backed Securities - Residential
Schedule of Held-to-maturity Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	59,446	40,832	1,616
Fair Value, Measurements, Recurring
Schedule of Held-to-maturity Securities [Line Items]
Equity Securities	1,579
Fair Value, Measurements, Recurring | Mortgage-Backed Securities - Residential | US Government-sponsored Enterprises Debt Securities
Schedule of Held-to-maturity Securities [Line Items]
Held-To-Maturity Securities, at Fair Value	53,850	57,887	68,729
Fair Value, Measurements, Recurring | Agency Securities | Mortgage-Backed Securities - Residential
Schedule of Held-to-maturity Securities [Line Items]
Held-To-Maturity Securities, at Fair Value	$ 2,483	$ 2,661	$ 3,121