Investment Securities Schedule of Held to Maturity Securities (Details) $ in Thousands	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	$ 335,907	$ 345,427
Held-To-Maturity Securities, at Fair Value	335,901	343,751
Gross Unrealized Gains	1,960	2,316
Gross Unrealized Losses	1,966	3,992
Held-To-Maturity Securities, Pledged as Collateral, at Fair Value	318,622	321,202
Maturities of Debt Securities, at Amortized Cost:
Within One Year	38,422
From 1 - 5 Years	135,001
From 5 - 10 Years	159,083
Over 10 Years	3,401
Maturities of Debt Securities, at Fair Value:
Within One Year	38,506
From 1 - 5 Years	135,869
From 5 - 10 Years	158,082
Over 10 Years	3,444
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	69,412	120,561
12 Months or Longer	68,409	12,363
Total	$ 137,821	$ 132,924
Number of Securities in a Continuous Loss Position	366	360
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 498	$ 3,298
12 Months or Longer	1,468	694
Total	1,966	3,992
State and Municipal Obligations [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	275,530	268,892
Held-To-Maturity Securities, at Fair Value	275,353	267,127
Gross Unrealized Gains	1,691	2,058
Gross Unrealized Losses	1,868	3,823
Maturities of Debt Securities, at Amortized Cost:
Within One Year	38,422
From 1 - 5 Years	80,789
From 5 - 10 Years	152,918
Over 10 Years	3,401
Maturities of Debt Securities, at Fair Value:
Within One Year	38,506
From 1 - 5 Years	81,499
From 5 - 10 Years	151,904
Over 10 Years	3,444
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	55,648	107,255
12 Months or Longer	65,152	12,363
Total	$ 120,800	$ 119,618
Number of Securities in a Continuous Loss Position	352	347
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 442	$ 3,129
12 Months or Longer	1,425	694
Total	1,867	3,823
Collateralized Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	60,377	75,535
Held-To-Maturity Securities, at Fair Value	60,548	75,624
Gross Unrealized Gains	269	258
Gross Unrealized Losses	98	169
Maturities of Debt Securities, at Amortized Cost:
Within One Year	0
From 1 - 5 Years	54,212
From 5 - 10 Years	6,165
Over 10 Years	0
Maturities of Debt Securities, at Fair Value:
Within One Year	0
From 1 - 5 Years	54,370
From 5 - 10 Years	6,178
Over 10 Years	0
Securities in a Continuous Loss Position, at Fair Value:
Less than 12 Months	13,764	13,306
12 Months or Longer	3,257	0
Total	$ 17,021	$ 13,306
Number of Securities in a Continuous Loss Position	14	13
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 56	$ 169
12 Months or Longer	43	0
Total	99	169
Corporate and Other Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	0	1,000
Held-To-Maturity Securities, at Fair Value	0	1,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	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
12 Months or Longer	0	0
Total	$ 0	$ 0
Number of Securities in a Continuous Loss Position	0	0
Unrealized Losses on Securities in a Continuous Loss Position:
Less than 12 Months	$ 0	$ 0
12 Months or Longer	0	0
Total	0	0
Collateralized Mortgage Backed Securities [Member] | Agency Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	2,680	3,206
Collateralized Mortgage Backed Securities [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-Maturity (Approximate Fair Value of $335,901 at December 31, 2017, and $343,751 at December 31, 2016)	57,697	72,329
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-To-Maturity Securities, at Fair Value	57,887	72,402
Fair Value, Measurements, Recurring [Member] | Agency Securities [Member] | Collateralized Mortgage Backed Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-To-Maturity Securities, at Fair Value	$ 2,661	$ 3,222