CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 226,507	$ 319,399
Short-term marketable securities	52,856	38,179
Accounts receivable, net of allowances aggregating $44,315 and $27,799, respectively	606,952	528,924
Unbilled accounts receivable	54,794	35,922
Deferred costs	18,770	20,445
Inventories and supplies	199,479	176,012
Prepaid expenses and other current assets	42,800	35,175
Total current assets	1,202,158	1,154,056
Property, plant and equipment, net	1,561,978	1,587,365
Other assets:
Goodwill	514,189	478,523
Permits and other intangibles, net	441,875	469,128
Other	18,121	17,498
Total other assets	974,185	965,149
Total assets	3,738,321	3,706,570
Current liabilities:
Current portion of long-term obligations	7,535	4,000
Accounts payable	276,461	224,231
Deferred revenue	61,843	67,822
Accrued expenses	233,405	187,982
Current portion of closure, post-closure and remedial liabilities	23,034	19,782
Total current liabilities	602,278	503,817
Other liabilities:
Closure and post-closure liabilities, less current portion of $9,592 and $6,444, respectively	60,339	54,593
Remedial liabilities, less current portion of $13,442 and $13,338, respectively	107,575	111,130
Long-term obligations, less current portion	1,565,021	1,625,537
Deferred taxes, unrecognized tax benefits and other long-term liabilities	233,352	223,291
Total other liabilities	1,966,287	2,014,551
Commitments and contingent liabilities (See Note 18)
Stockholders' equity:
Common stock, $.01 par value: Authorized 80,000,000 shares; issued and outstanding 56,501,190 and 57,297,978 shares, respectively	558	565
Additional paid-in capital	655,415	686,962
Accumulated other comprehensive loss	(223,371)	(172,407)
Accumulated earnings	737,154	673,082
Total stockholders' equity	1,169,756	1,188,202
Total liabilities and stockholders' equity	$ 3,738,321	$ 3,706,570