Shareholders' Equity (Regulatory Captial Requirements) (Details) - USD ($) $ in Thousands		Sep. 30, 2018	Dec. 31, 2017
Corporation [Member]
Total Capital (to Risk-Weighted Assets):
Total Capital		$ 445,448	$ 416,038
Total Capital to Risk-Weighted Assets		12.77%	12.45%
Total Capital for Capital Adequacy Purposes		$ 279,165	$ 267,365
Total Capital for Capital Adequacy Purposes to Risk-Weighted Assets		8.00%	8.00%
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital		$ 418,649	$ 389,289
Tier 1 Capital to Risk Weighted-Assets		12.00%	11.65%
Tier 1 Capital Required For Capital Adequacy Purposes		$ 209,374	$ 200,524
Tier 1 Capital Required for Capital Adequacy Purposes to Risk Weighted-Assets		6.00%	6.00%
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital		$ 396,651	$ 367,291
Common Equity Tier 1 Capital to Risk Weighted Assets		11.37%	10.99%
Common Equity Tier 1 Capital Required for Capital Adequacy		$ 157,031	$ 150,383
Common Equity Tier 1 Capital for Capital Adequacy to Risk Weighted Assets		4.50%	4.50%
Tier 1 Capital (to Average Assets):
Tier 1 Leverage Capital	[1]	$ 418,649	$ 389,289
Tier 1 Leverage Capital to Average Assets	[1]	8.91%	8.79%
Tier 1 Leverage Capital Required for Capital Adequacy Purposes	[1]	$ 187,898	$ 177,089
Tier 1 Leverage Capital Required for Capital Adequacy Purposes to Average Assets	[1]	4.00%	4.00%
Bank [Member]
Total Capital (to Risk-Weighted Assets):
Total Capital		$ 442,337	$ 413,593
Total Capital to Risk-Weighted Assets		12.68%	12.38%
Total Capital for Capital Adequacy Purposes		$ 279,145	$ 267,338
Total Capital for Capital Adequacy Purposes to Risk-Weighted Assets		8.00%	8.00%
Total Capital To Be Well Capitalized		$ 348,931	$ 334,172
Total Capital To Be Well Capitalized to Risk Weighted-Assets		10.00%	10.00%
Tier 1 Capital (to Risk-Weighted Assets):
Tier 1 Capital		$ 415,538	$ 386,844
Tier 1 Capital to Risk Weighted-Assets		11.91%	11.58%
Tier 1 Capital Required For Capital Adequacy Purposes		$ 209,358	$ 200,503
Tier 1 Capital Required for Capital Adequacy Purposes to Risk Weighted-Assets		6.00%	6.00%
Tier 1 Capital Required To Be Well Capitalized		$ 279,145	$ 267,338
Tier 1 Capital Required To Be Well Capitalized to Risk Weighted-Assets		8.00%	8.00%
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital		$ 415,538	$ 386,844
Common Equity Tier 1 Capital to Risk Weighted Assets		11.91%	11.58%
Common Equity Tier 1 Capital Required for Capital Adequacy		$ 157,019	$ 150,378
Common Equity Tier 1 Capital for Capital Adequacy to Risk Weighted Assets		4.50%	4.50%
Common Equity Tier 1 Capital Required to be Well Capitalized		$ 226,805	$ 217,212
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk Weighted Assets		6.50%	6.50%
Tier 1 Capital (to Average Assets):
Tier 1 Leverage Capital	[1]	$ 415,538	$ 386,844
Tier 1 Leverage Capital to Average Assets	[1]	8.85%	8.74%
Tier 1 Leverage Capital Required for Capital Adequacy Purposes	[1]	$ 187,858	$ 177,048
Tier 1 Leverage Capital Required for Capital Adequacy Purposes to Average Assets	[1]	4.00%	4.00%
Tier 1 Leverage Capital Required To Be Well Capitalized	[1]	$ 234,822	$ 221,310
Tier 1 Leverage Capital Required To Be Well Capitalized to Average Assets	[1]	5.00%	5.00%

[1] Leverage ratio.