CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, accumulated provision for doubtful accounts	$ 8,648	$ 7,780
Common stock, par value (in dollars per share)	$ 0	$ 0
Common stock, authorized (in shares)	320,000,000	320,000,000
Common stock, issued (in shares)	257,225,000	267,871,000
Treasury stock (in shares)	2,753,000	3,551,000
Treasury stock, held in rabbi trust (in shares)	0	253,145