Condensed Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Customer receivables, allowances	$ 8,443	$ 8,346
Common stock, par value	$ 0.10	$ 0.10
Common stock, shares authorized	140,000,000	140,000,000
Common stock, shares outstanding	82,387,823	82,416,657