Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Condensed Consolidated Balance Sheets [Abstract]
Accounts receivable, reserves	$ 4,808	$ 4,576
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	104,676,000	104,275,000
Common stock, shares, outstanding	86,997,000	87,104,000
Deferred stock units, outstanding	217,000	229,000
Treasury stock, shares	17,679,000	17,171,000