Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, accumulated provision for doubtful accounts	$ 5,663	$ 6,923
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, authorized shares (in shares)	320,000,000	320,000,000
Common stock, shares issued (in shares)	177,896,000	177,896,000
Treasury stock, shares at cost (in shares)	4,553,000	5,069,000
Treasury stock, shares held in rabbi trust (in shares)	251,000	226,000