Consolidated Balance Sheets Parenthetical - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,025	$ 5,879
Common stock stated value per share (USD per share)	$ 20	$ 20
Authorized	50,000,000	50,000,000
Issued to voting trustees	14,606,830	13,668,055
Issued to shareholders	2,850,551	2,721,926
In treasury, at cost	(18,854)	(65,890)
Outstanding Common Stock	17,438,527	16,324,091
Common Stock, Shares Subscribed	896,456	878,608
Subscripton Receivable	(896,456)	(878,608)