Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciles the accumulated liability for the benefit obligation
Beginning balance	$ 2,957	$ 2,760	$ 2,549
Benefit expense	387	359	369
Benefit payments	(162)	(162)	(158)
Ending balance	$ 3,182	$ 2,957	$ 2,760