CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 44,749	$ 38,711
Closure and post-closure liabilities, current portion	13,903	7,283
Remedial liabilities, current portion	$ 12,190	$ 16,018
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)	54,772,696	55,797,734
Common stock, outstanding shares (in shares)	54,772,696	55,797,734