Condensed Consolidated Balance Sheets Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,866	$ 5,879
Common, stated value per share	$ 20	$ 20
Authorized	50,000,000	50,000,000
Issued to voting trustees	14,038,439	13,668,055
Issued to shareholders	2,752,320	2,721,926
In treasury, at cost	(198,253)	(65,890)
Outstanding common stock	16,592,506	16,324,091