Condensed Consolidated Balance Sheets Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,695	$ 5,025
Common, stated value per share	$ 20	$ 20
Authorized	50,000,000	50,000,000
Issued to voting trustees	14,717,825	14,606,830
Issued to shareholders	3,469,173	2,850,551
In treasury, at cost	(590,066)	(18,854)
Outstanding common stock	17,596,932	17,438,527