Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Accounts receivable, accumulated provision for doubtful accounts	$ 6,179	$ 8,648
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)	257,003,000	257,225,000
Treasury stock, shares at cost (in shares)	1,833,000	2,753,000