Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Current Assets:
Cash and cash equivalents	$ 1,422,373	$ 1,446,364	$ 55,418
Accounts receivable, net	466,465	487,240	479,215
Inventories, net	606,794	600,591	537,000
Other current assets	106,298	96,965	51,609
Total Current Assets	2,601,930	2,631,160	1,123,242
Property, plant and equipment	6,523,364	6,498,067	6,211,813
Allowances for depreciation, depletion and amortization	(2,940,870)	(2,905,254)	(2,744,168)
Net property, plant and equipment	3,582,494	3,592,813	3,467,645
Goodwill	2,160,290	2,160,290	2,159,398
Operating permits, net	437,438	439,116	440,411
Other intangibles, net	61,338	67,233	67,318
Other noncurrent assets	104,560	101,899	135,777
Total Assets	8,948,050	8,992,511	7,393,791
Current Liabilities:
Accounts payable	162,328	183,638	188,399
Accrued salaries, benefits and payroll taxes	23,329	44,255	22,760
Pension and postretirement benefits	12,812	13,652	8,136
Accrued insurance and other taxes	52,413	64,958	49,535
Current maturities of long-term debt and short-term facilities	300,006	299,909	290,048
Accrued interest	39,720	19,825	23,649
Other current liabilities	60,371	67,979	49,031
Total Current Liabilities	650,979	694,216	631,558
Long-term debt	2,728,102	2,727,294	1,556,246
Pension, postretirement and postemployment benefits	248,501	244,043	252,568
Deferred income taxes, net	413,570	410,723	667,160
Other noncurrent liabilities	227,068	233,758	210,305
Total Liabilities	4,268,220	4,310,034	3,317,837
Equity:
Common stock, par value $0.01 per share	628	628	626
Preferred stock, par value $0.01 per share
Additional paid-in capital	3,381,280	3,368,007	3,349,813
Accumulated other comprehensive loss	(127,485)	(129,104)	(128,425)
Retained earnings	1,422,207	1,440,069	851,354
Total Shareholders' Equity	4,676,630	4,679,600	4,073,368
Noncontrolling interests	3,200	2,877	2,586
Total Equity	4,679,830	4,682,477	4,075,954
Total Liabilities and Equity	$ 8,948,050	$ 8,992,511	$ 7,393,791