CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 28,537	$ 29,249
Closure and post-closure liabilities, current portion	4,077	6,220
Remedial liabilities, current portion	$ 15,439	$ 13,796
Common stock, par value (in USD per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	56,926,549	57,297,978
Common stock, outstanding shares (in shares)	56,926,549	57,297,978