Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 347,580	$ 305,372
Short term investments	122,505	88,072
Restricted cash	68,984	71,050
Trade accounts receivable	150,399	184,483
Other receivables	22,482	19,877
Inventories	125,194	113,462
Other current assets	74,063	96,306
Total current assets	911,207	878,622
Property, plant and equipment, net	1,027,288	1,053,603
Other assets
Equity investments	104,144	96,074
Other noncurrent assets	102,277	108,298
Total other assets	206,421	204,372
Total assets	2,144,916	2,136,597
Current Liabilities
Accounts payable	103,130	95,953
Accrued expenses and other current liabilities	172,898	205,240
Current maturities of debt	7,898	11,038
Total current liabilities	283,926	312,231
Long-term debt	318,030	351,841
Asset retirement obligations	339,865	337,227
Accrued pension benefits	37,510	38,884
Accrued postretirement benefits other than pension	101,786	101,445
Accrued workers’ compensation	184,792	184,568
Other noncurrent liabilities	77,301	63,824
Total liabilities	1,343,210	1,390,020
Stockholders' equity
Common stock, $0.01 par value, authorized 300,000 shares, issued 25,021 shares and 25,002 shares at March 31, 2017 and December 31, 2016, respectively	250	250
Paid-in capital	692,253	688,424
Retained earnings	85,117	33,449
Accumulated other comprehensive income	24,086	24,454
Total stockholders’ equity	801,706	746,577
Total liabilities and stockholders’ equity	$ 2,144,916	$ 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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.