Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 186,811	$ 143,750
Restricted cash and cash equivalents	365
Short-term investments	14,500
Accounts receivable, net	88,074	80,570
Inventories	56,586	55,872
Supplies, prepaid items and other:
Prepaid insurance	13,752	15,073
Precious metals	12,838	14,927
Supplies	15,927	13,523
Prepaid and refundable income taxes	7,387	12,644
Other	5,438	3,867
Total supplies, prepaid items and other	55,342	60,034
Deferred income taxes	17,204	13,613
Total current assets	418,882	353,839
Property, plant and equipment, net	619,205	416,801
Other assets:
Noncurrent restricted cash and cash equivalents	45,969	80,974
Noncurrent restricted investments	25,000	209,990
Capitalized software costs, net	12,595	4,927
Other, net	15,354	16,566
Total other assets	98,918	312,457
Total assets	1,137,005	1,083,097
Current liabilities:
Accounts payable	81,456	61,775
Short-term financing	11,955	13,749
Accrued and other liabilities	51,166	49,107
Current portion of long-term debt	10,680	9,262
Total current liabilities	155,257	133,893
Long-term debt	446,638	453,705
Noncurrent accrued and other liabilities	17,934	17,086
Deferred income taxes	83,128	66,698
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock, $.10 par value; 75,000,000 shares authorized, 26,968,212 shares issued (26,846,470 shares at December 31, 2013)	2,697	2,685
Capital in excess of par value	170,537	167,550
Retained earnings	286,188	266,854
Stockholders equity including treasury stock	462,422	440,089
Less treasury stock, at cost:
Common stock, 4,320,462 shares	28,374	28,374
Total stockholders' equity	434,048	411,715
Total Liabilities and Stockholders' equity	1,137,005	1,083,097
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