CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 186,352	$ 319,399
Short-term marketable securities	37,792	38,179
Accounts receivable, net of allowances aggregating $29,145 and $27,799, respectively	551,841	528,924
Unbilled accounts receivable	63,375	35,922
Deferred costs	20,847	20,445
Inventories and supplies	181,438	176,012
Prepaid expenses and other current assets	38,177	35,175
Total current assets	1,079,822	1,154,056
Property, plant and equipment, net	1,631,648	1,587,365
Other assets:
Goodwill	492,705	478,523
Permits and other intangibles, net	464,635	469,128
Other	16,006	17,498
Total other assets	973,346	965,149
Total assets	3,684,816	3,706,570
Current liabilities:
Current portion of long-term obligations	4,000	4,000
Accounts payable	237,953	224,231
Deferred revenue	68,748	67,822
Accrued expenses	194,160	187,982
Current portion of closure, post-closure and remedial liabilities	19,823	19,782
Total current liabilities	524,684	503,817
Other liabilities:
Closure and post-closure liabilities, less current portion of $5,519 and $6,444, respectively	58,561	54,593
Remedial liabilities, less current portion of $14,304 and $13,338, respectively	108,143	111,130
Long-term obligations, less current portion	1,625,259	1,625,537
Deferred taxes, unrecognized tax benefits and other long-term liabilities	222,643	223,291
Total other liabilities	2,014,606	2,014,551
Commitments and contingent liabilities (See Note 16)
Stockholders’ equity:
Authorized 80,000,000; shares issued and outstanding 56,244,601 and 56,501,190 shares, respectively	562	565
Additional paid-in capital	675,230	686,962
Accumulated other comprehensive loss	(189,153)	(172,407)
Accumulated earnings	658,887	673,082
Total stockholders’ equity	1,145,526	1,188,202
Total liabilities and stockholders’ equity	$ 3,684,816	$ 3,706,570