Capital Ratios (Narrative) (Details)		6 Months Ended
		Jun. 30, 2018		Dec. 31, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Total Risk-based Capital Ratio: Ratio		14.51%
Capital Ratios, Basel III, Capital Conservation Buffer				1.25%	0.625%
Capital Ratios, Basel III, Capital Conservation Buffer, Year Two		1.875%
Capital Ratios, Basel III, Capital Conservation Buffer, Year Three		2.50%
Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	[1]	6.50%
Tier 1 Risk-based Capital Ratio: Well Capitalized Minimum: Ratio		8.00%	[2]	6.00%
Tier 1 Leverage Ratio: Well Capitalized Minimum: Ratio	[3]	5.00%
Total Risk-based Capital Ratio: Well Capitalized Minimum: Ratio	[4]	10.00%
Capital ratios, capital conservation buffer		6.51%
Total Risk-based Capital Ratio: Ratio	[4]	14.39%		15.19%

[1] Common equity Tier 1 capital/ total risk-weighted assets

[2] Tier 1 capital / total risk-weighted assets

[3] Tier 1 capital / average quarterly assets

[4] Total risk-based capital / total risk-weighted assets