Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 333,548	$ 305,372
Short term investments	159,822	88,072
Restricted cash	41,755	71,050
Trade accounts receivable	190,256	184,483
Other receivables	21,504	19,877
Inventories	137,056	113,462
Other current assets	61,474	96,306
Total current assets	945,415	878,622
Property, plant and equipment, net	1,007,570	1,053,603
Other assets
Equity investments	104,015	96,074
Other noncurrent assets	75,058	108,298
Total other assets	179,073	204,372
Total assets	2,132,058	2,136,597
Current Liabilities
Accounts payable	127,059	95,953
Accrued expenses and other current liabilities	169,533	205,240
Current maturities of debt	7,414	11,038
Total current liabilities	304,006	312,231
Long-term debt	315,639	351,841
Asset retirement obligations	342,680	337,227
Accrued pension benefits	32,092	38,884
Accrued postretirement benefits other than pension	101,407	101,445
Accrued workers’ compensation	186,128	184,568
Other noncurrent liabilities	65,048	63,824
Total liabilities	1,347,000	1,390,020
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 25,021 shares and 25,002 shares at June 30, 2017 and December 31, 2016, respectively	250	250
Paid-in capital	694,780	688,424
Retained earnings	113,574	33,449
Treasury stock, 711 shares at June 30, 2017, at cost	(51,043)	0
Accumulated other comprehensive income	27,497	24,454
Total stockholders’ equity	785,058	746,577
Total liabilities and stockholders’ equity	$ 2,132,058	$ 2,136,597

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.