CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 162,783	$ 143,750
Accounts receivable, net	90,610	80,570
Inventories:
Finished goods	26,819	29,163
Work in progress	2,835	2,838
Raw materials	27,581	23,871
Total inventories	57,235	55,872
Supplies, prepaid items and other:
Prepaid insurance	11,301	15,073
Precious metals	12,986	14,927
Supplies	14,435	13,523
Prepaid income taxes	4,403	12,644
Other	5,517	3,867
Total supplies, prepaid items and other	48,642	60,034
Deferred income taxes	11,409	13,613
Total current assets	370,679	353,839
Property, plant and equipment, net	451,184	416,801
Other assets:
Noncurrent restricted cash and cash equivalents	246,080	80,974
Noncurrent restricted investments		209,990
Debt issuance costs, net	7,657	8,027
Other, net	14,705	13,466
Total other assets	268,442	312,457
Total assets	1,090,305	1,083,097
Current liabilities:
Accounts payable	68,630	61,775
Short-term financing	9,676	13,749
Accrued and other liabilities	38,318	49,107
Current portion of long-term debt	9,748	9,262
Total current liabilities	126,372	133,893
Long-term debt	452,136	453,705
Noncurrent accrued and other liabilities	17,437	17,086
Deferred income taxes	70,493	66,698
Commitments and contingencies (Note 9)
Stockholders' equity:
Common stock, $.10 par value; 75,000,000 shares authorized, 26,855,450 shares issued (26,846,470 at December 31, 2013)	2,686	2,685
Capital in excess of par value	168,360	167,550
Retained earnings	278,195	266,854
Stockholders equity including treasury stock	452,241	440,089
Less treasury stock, at cost:
Common stock, 4,320,462 shares	28,374	28,374
Total stockholders' equity	423,867	411,715
Total Liabilities and Stockholders' equity	1,090,305	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