CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 452,575	$ 519,101
Short-term marketable securities	81,724	51,857
Accounts receivable, net of allowances aggregating $40,140 and $44,749, respectively	792,734	611,534
Unbilled accounts receivable	94,963	55,681
Inventories and supplies	250,692	220,498
Prepaid expenses and other current assets	68,483	67,051
Total current assets	1,741,171	1,525,722
Property, plant and equipment, net	1,863,175	1,525,298
Other assets:
Operating lease right-of-use assets	161,797	150,341
Goodwill	1,227,042	527,023
Permits and other intangibles, net	644,912	386,620
Other	15,602	16,516
Total other assets	2,049,353	1,080,500
Total assets	5,653,699	4,131,520
Current liabilities:
Current portion of long-term debt	17,535	7,535
Accounts payable	359,866	195,878
Deferred revenue	83,749	74,066
Accrued expenses and other current liabilities	391,414	295,823
Current portion of closure, post-closure and remedial liabilities	25,136	26,093
Current portion of operating lease liabilities	47,614	36,750
Total current liabilities	925,314	636,145
Other liabilities:
Closure and post-closure liabilities, less current portion of $12,015 and $13,903, respectively	87,088	74,023
Remedial liabilities, less current portion of $13,121 and $12,190, respectively	98,752	102,623
Long-term debt, less current portion	2,517,024	1,549,641
Operating lease liabilities, less current portion	117,991	114,258
Deferred tax liabilities	314,853	230,097
Other long-term liabilities	78,790	83,182
Total other liabilities	3,214,498	2,153,824
Commitments and contingent liabilities (See Note 17)
Stockholders' equity:
Common stock	544	548
Additional paid-in capital	536,377	582,749
Accumulated other comprehensive loss	(196,012)	(211,477)
Accumulated earnings	1,172,978	969,731
Total stockholders' equity	1,513,887	1,341,551
Total liabilities and stockholders' equity	$ 5,653,699	$ 4,131,520