CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 319,399	$ 306,997
Short-term marketable securities	38,179	0
Accounts receivable, net of allowances aggregating $27,799 and $29,249, respectively	528,924	496,226
Unbilled accounts receivable	35,922	36,190
Deferred costs	20,445	18,914
Inventories and supplies	176,012	178,428
Prepaid expenses and other current assets	35,175	56,116
Total current assets	1,154,056	1,092,871
Property, plant and equipment, net	1,587,365	1,611,827
Other assets:
Goodwill	478,523	465,154
Permits and other intangibles, net	469,128	498,721
Other	17,498	13,347
Total other assets	965,149	977,222
Total assets	3,706,570	3,681,920
Current liabilities:
Current portion of long-term obligations	4,000	0
Accounts payable	224,231	229,534
Deferred revenue	67,822	64,397
Accrued expenses	187,982	190,721
Current portion of closure, post-closure and remedial liabilities	19,782	20,016
Total current liabilities	503,817	504,668
Other liabilities:
Closure and post-closure liabilities, less current portion of $6,444 and $6,220, respectively	54,593	52,111
Remedial liabilities, less current portion of $13,338 and $13,796, respectively	111,130	114,211
Long-term obligations, less current portion	1,625,537	1,633,272
Deferred taxes, unrecognized tax benefits and other long-term liabilities	223,291	293,417
Total other liabilities	2,014,551	2,093,011
Commitments and contingent liabilities (See Note 17)
Stockholders' equity:
Common stock, $.01 par value: Authorized 80,000,000 shares; issued and outstanding 56,501,190 and 57,297,978 shares, respectively	565	573
Shares held under employee participation plan	0	(469)
Additional paid-in capital	686,962	725,670
Accumulated other comprehensive loss	(172,407)	(214,326)
Accumulated earnings	673,082	572,793
Total stockholders' equity	1,188,202	1,084,241
Total liabilities and stockholders' equity	$ 3,706,570	$ 3,681,920