Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, reserves	$ 4,689	$ 4,576
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	120,000,000	120,000,000
Common stock, shares issued (in shares)	104,847,000	104,275,000
Common stock, shares outstanding (in shares)	86,642,000	87,104,000
Deferred stock units, outstanding (in shares)	162,000	229,000
Treasury stock, shares (in shares)	18,195,000	17,171,000