Condensed Consolidated Balance Sheets Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 5,658	$ 5,025
Common, stated value per share	$ 20	$ 20
Authorized	50,000,000	50,000,000
Issued to voting trustees	14,612,710	14,606,830
Issued to shareholders	3,432,406	2,850,551
In treasury, at cost	(349,480)	(18,854)
Outstanding common stock	17,695,636	17,438,527