CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 45,037	$ 60,017
Accounts receivable, net	75,284	51,299
Inventories:
Finished goods	17,323	19,036
Raw materials	3,698	3,903
Total inventories	21,021	22,939
Supplies, prepaid items and other:
Prepaid insurance	8,191	11,217
Precious metals	7,463	8,648
Supplies	24,983	24,100
Prepaid and refundable income taxes	1,078	1,193
Other	2,966	1,733
Total supplies, prepaid items and other	44,681	46,891
Total current assets	186,023	181,146
Property, plant and equipment, net	1,068,892	1,078,958
Intangible and other assets, net	9,584	10,316
Total assets	1,264,499	1,270,420
Current liabilities:
Accounts payable	53,338	54,246
Short-term financing	5,428	8,218
Accrued and other liabilities	52,779	44,037
Current portion of long-term debt	11,752	13,745
Total current liabilities	123,297	120,246
Long-term debt, net	405,520	406,475
Noncurrent accrued and other liabilities	10,431	12,326
Deferred income taxes	91,529	93,831
Commitments and contingencies (Note 8)
Stockholders' equity:
Common stock, $.10 par value; 75,000,000 shares authorized, 31,280,685 shares issued	3,128	3,128
Capital in excess of par value	192,433	192,172
Retained earnings	302,240	314,301
Stockholders equity including treasury stock	500,801	512,601
Less treasury stock, at cost:
Common stock, 2,875,582 shares (3,004,855 shares at December 31, 2016)	19,243	20,088
Total stockholders' equity	481,558	492,513
Total Liabilities and Stockholders' equity	1,264,499	1,270,420
Series E Preferred Stock [Member]
Redeemable preferred stocks:
Redeemable preferred stock, value	152,164	145,029
Series B Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value	2,000	2,000
Series D Preferred Stock [Member]
Stockholders' equity:
Preferred stock, value	$ 1,000	$ 1,000