CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 29,145	$ 27,799
Closure and post-closure liabilities, current portion	5,519	6,444
Remedial liabilities, current portion	$ 14,304	$ 13,338
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)	56,244,601	56,501,190
Common stock, outstanding shares (in shares)	56,244,601	56,501,190