Guarantees and Commitments (Narrative) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2018 USD ($) Apartment	Dec. 31, 2017 USD ($)
Commitments, Contingencies and Guarantees [Line Items]
Number of apartments under the project | Apartment	37
Limited partner capital contribution commitment	$ 7,593,000
Project investment amortization period	10 years
Annual LIHTCs mount awarded for the project	$ 863,000
Total anticipated LIHTCs amount under the housing project	8,629,000
Financial Standby Letters of Credit [Member]
Commitments, Contingencies and Guarantees [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 20,647,000	$ 20,496,000