CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 44,407	$ 44,749
Closure and post-closure liabilities, current portion	11,887	13,903
Remedial liabilities, current portion	$ 15,009	$ 12,190
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	80,000,000	80,000,000
Common stock, issued shares (in shares)	54,550,817	54,772,696
Common stock, outstanding shares (in shares)	54,550,817	54,772,696