Shareholders' Equity, Stock Repurchase Program, Dividends and Issuance of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Stock Repurchased [Abstract]
Approved funds available for common stock repurchase program		$ 20,000
Number of shares of stock purchased (in shares)		0	0
Total consideration for shares to be purchased	$ 31,200	$ 31,152
Per share price of shares issued (in dollars per share)	$ 700
Issuance of common stock for contribution to non-qualified defined contribution retirement plans (in shares)		13,520	4,975
Shares issued to individuals (in shares)		2,400
Minimum [Member]
Stock Repurchased [Abstract]
Per share price of shares issued (in dollars per share)		$ 635	$ 590
Maximum [Member]
Stock Repurchased [Abstract]
Per share price of shares issued (in dollars per share)		$ 690	$ 595