Fair Value of Assets and Liabilities (Details 2) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) Security	Mar. 31, 2017 USD ($) Security	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Breakdown of trust preferred securities
Number considered OTTI | Security	1
Life-to-date impairment recognized in earnings	$ 140	$ 140	$ 140	$ 140
Trust preferred securities
Breakdown of trust preferred securities
Total number of trust preferred securities | Security	2	2
Par value, trust preferred securities	$ 1,969	$ 1,939
Number not considered OTTI | Security	1	1
Par value, trust preferred securities not considered OTTI	$ 933	$ 903
Number considered OTTI | Security	1	1
Par value, trust preferred securities considered OTTI	$ 1,036	$ 1,036
Life-to-date impairment recognized in earnings	140	140	140	$ 140
Life-to-date impairment recognized in other comprehensive income	528	723	$ 723
Total life-to-date impairment	$ 668	$ 863