CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Account receivable, allowances aggregating	$ 36,398	$ 44,315
Closure and post-closure liabilities, current portion	13,491	9,592
Remedial liabilities, current portion	$ 17,256	$ 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)	55,859,402	55,847,261
Common stock, outstanding shares (in shares)	55,859,402	55,847,261