CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 167,371	$ 226,507
Short-term marketable securities	57,477	52,856
Accounts receivable, net of allowances aggregating $37,409 and $44,315, respectively	613,507	606,952
Unbilled accounts receivable	42,513	54,794
Deferred costs	20,515	18,770
Inventories and supplies	200,814	199,479
Prepaid expenses and other current assets	45,925	42,800
Total current assets	1,148,122	1,202,158
Property, plant and equipment, net	1,588,613	1,561,978
Other assets:
Operating lease right-of-use asset	170,550
Goodwill	517,910	514,189
Permits and other intangibles, net	438,958	441,875
Other	17,901	18,121
Total other assets	1,145,319	974,185
Total assets	3,882,054	3,738,321
Current liabilities:
Current portion of long-term obligations	7,535	7,535
Accounts payable	242,260	276,461
Deferred revenue	67,557	61,843
Accrued expenses	208,386	233,405
Current portion of closure, post-closure and remedial liabilities	27,914	23,034
Current portion of operating lease liability	43,858
Total current liabilities	597,510	602,278
Other liabilities:
Closure and post-closure liabilities, less current portion of $12,337 and $9,592, respectively	62,084	60,339
Remedial liabilities, less current portion of $15,577 and $13,442, respectively	103,384	107,575
Long-term obligations, less current portion	1,564,005	1,565,021
Operating lease liability, less current portion	128,689
Deferred taxes, unrecognized tax benefits and other long-term liabilities	254,417	233,352
Total other liabilities	2,112,579	1,966,287
Commitments and contingent liabilities (See Note 16)
Stockholders’ equity:
Authorized 80,000,000; shares issued and outstanding 55,827,714 and 55,847,261 shares, respectively	558	558
Additional paid-in capital	652,624	655,415
Accumulated other comprehensive loss	(219,347)	(223,371)
Accumulated earnings	738,130	737,154
Total stockholders’ equity	1,171,965	1,169,756
Total liabilities and stockholders’ equity	$ 3,882,054	$ 3,738,321