CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 339,584	$ 452,575
Short-term marketable securities	75,364	81,724
Accounts receivable, net of allowances aggregating $45,373 and $40,140, respectively	900,273	792,734
Unbilled accounts receivable	123,945	94,963
Inventories and supplies	264,733	250,692
Prepaid expenses and other current assets	103,349	68,483
Total current assets	1,807,248	1,741,171
Property, plant and equipment, net	1,881,542	1,863,175
Other assets:
Operating lease right-of-use assets	156,811	161,797
Goodwill	1,221,399	1,227,042
Permits and other intangibles, net	633,445	644,912
Other	25,812	15,602
Total other assets	2,037,467	2,049,353
Total assets	5,726,257	5,653,699
Current liabilities:
Current portion of long-term debt	17,535	17,535
Accounts payable	394,152	359,866
Deferred revenue	90,116	83,749
Accrued expenses and other current liabilities	338,835	391,414
Current portion of closure, post-closure and remedial liabilities	26,393	25,136
Current portion of operating lease liabilities	47,108	47,614
Total current liabilities	914,139	925,314
Other liabilities:
Closure and post-closure liabilities, less current portion of $7,808 and $12,015, respectively	92,891	87,088
Remedial liabilities, less current portion of $18,585 and $13,121, respectively	106,144	98,752
Long-term debt, less current portion	2,513,944	2,517,024
Operating lease liabilities, less current portion	113,059	117,991
Deferred tax liabilities	312,668	314,853
Other long-term liabilities	80,175	78,790
Total other liabilities	3,218,881	3,214,498
Commitments and contingent liabilities (See Note 16)
Stockholders’ equity:
Common stock	544	544
Additional paid-in capital	536,564	536,377
Accumulated other comprehensive loss	(162,163)	(196,012)
Accumulated earnings	1,218,292	1,172,978
Total stockholders’ equity	1,593,237	1,513,887
Total liabilities and stockholders’ equity	$ 5,726,257	$ 5,653,699