Retirement Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Retirement Benefits [Abstract]
Automatic Annual Contribution Employees Hired Before January 1, 2009 Benefit Reduction Under Certain Amendments Minimum, percent	5.00%
Automatic Annual Contribution Employees Hired Before January 1, 2009 Due Benefit Reduction Under Certain Amendments Maximum, percent	7.00%
Employer's matching contribution to 401(k) of employees hired on or after January 1, 2009, percent	50.00%
Maximum annual contribution per employee, percent	3.00%
Funding and administrative costs of noncontributory defined benefit retirement plan and 401(k) plan [Abstract]
401(k) plan	$ 110	$ 102
Qualified noncontributory defined benefit retirement plan [Member]
Funding and administrative costs of noncontributory defined benefit retirement plan and 401(k) plan [Abstract]
Qualified noncontributory defined benefit retirement plan	261	260
Components of net periodic pension cost [Abstract]
Service cost	0	0
Interest cost	17	17
Amortization of unrecognized net loss	4	0
Net periodic pension cost	21	$ 17
Recognized in accumulated other comprehensive income [Abstract]
Net actuarial (gain) loss	166		$ 141
Past service cost	0		0
Total recognized, net of tax	$ 166		$ 141