Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Consolidated Balance Sheets [Abstract]
Accounts receivable, reserves	$ 4,576	$ 4,523
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	104,275,000	103,341,000
Deferred stock units, outstanding	229,000	231,000
Treasury stock, shares	17,171,000	15,367,000