Subsequent Events (Details) - $ / shares		12 Months Ended
	Mar. 15, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Issued [Abstract]
Shares issued to non-qualified defined contribution retirement plans (in shares)		13,520	4,975
Subsequent Event [Member]
Stock Issued [Abstract]
Shares issued to non-qualified defined contribution retirement plans (in shares)	3,586
Share price of shares issued (in dollars per share)	$ 715