Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating activities:
Net income	$ 11,094	$ 12,572
Non-cash elements included in net income:
Depreciation, depletion and amortization	14,711	11,269
Gain on disposition of properties, plants, equipment, and mineral interests	(125)	(28)
Provision for reclamation and closure costs	591	1,427
Stock compensation	798	558
Deferred income taxes	3,990	2,826
Amortization of loan origination fees	135	100
(Gain) loss on derivative contracts	(19,620)	12,140
Other non-cash (gains) charges, net	(11)	270
Change in assets and liabilities:
Accounts receivable	4,708	8,014
Inventories	(5,108)	1,948
Other current and non-current assets	382	549
Accounts payable and accrued liabilities	(2,712)	(5,580)
Accrued payroll and related benefits	5,046	(3,870)
Accrued taxes	(2,497)	2,890
Accrued reclamation and closure costs and other non-current liabilities	(22)	(3,659)
Cash provided by operating activities	11,360	41,426
Investing activities:
Additions to properties, plants, equipment and mineral interests	(25,753)	(24,652)
Proceeds from disposition of properties, plants and equipment	126	35
Purchases of investments	(2,562)
Changes in restricted cash and investment balances	(12)
Net cash used in investing activities	(28,201)	(24,617)
Financing activities:
Acquisition of treasury shares	(286)
Dividends paid to common shareholders	(3,565)	(3,566)
Dividends paid to preferred shareholders	(138)	(138)
Repayments of capital leases	(1,540)	(1,064)
Net cash (used) provided by financing activities	(5,529)	(4,768)
Change in cash and cash equivalents:
Net increase in cash and cash equivalents	(22,370)	12,041
Cash and cash equivalents at beginning of period	190,984	266,463
Cash and cash equivalents at end of period	168,614	278,504
Significant non-cash investing and financing activities:
Addition of capital lease obligations	6,725	4,417
Accounts payable change relating to capital additions	$ (6,529)	$ (2,126)