CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 37,409	$ 44,315
Closure and post-closure liabilities, current portion	12,337	9,592
Remedial liabilities, current portion	$ 15,577	$ 13,442
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)	55,827,714	55,847,261
Common stock, outstanding shares (in shares)	55,827,714	55,847,261