Supplementary Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Jun. 30, 2013	Sep. 30, 2013		Sep. 30, 2012
Change in working capital accounts:
Accounts receivable	$ 10.8		$ 24.3			$ 7.9		$ 33.8
Product inventory	(21.0)		(33.4)			(16.6)		(68.3)
Material and supplies inventory	(14.3)		(1.0)			(20.4)		(1.6)
Prepaid expenses and other current assets	6.8		(0.1)			(2.4)		0.5
Income and mining taxes receivable	1.7		(0.7)			10.1		(6.0)
Accounts payable and accrued liabilities	16.5		2.3			10.5		(3.4)
Income, mining and other taxes payable	(1.1)		0.5			(1.5)		(0.5)
Non-cash property, plant and equipment	0.8		3.2			0.8		3.2
Change in working capital accounts, total	(0.2)		4.9			11.6		42.3
Cash interest paid	19.1	[1]	1.4	[1]		54.5	[1]	14.8	[1]
Income and mining taxes paid, net	1.4	[2]	(7.8)	[2]		1.7	[2]	3.3	[2]
Proceeds from Income Tax Refunds	4.1				3.1	9.0
Investing activities
Acquisition of property, plant and equipment under the Equipment Facility	0		(51.0)			0		(54.7)
Change in capital expenditure accrual	0		(33.6)			0		(13.4)
Other investing adjustments	24.2	[3]	0	[3]		73.7	[3]	0	[3]
Capital leases	$ 0	[4]	$ 6.6	[4]		$ 0	[4]	$ 10.3	[4]

[1] For the three and nine months ended September 30, 2013, the cash interest paid of $19.1 million and $54.5 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9. For the three and nine months ended September 30, 2012, the cash interest paid of $1.4 million and $14.8 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9.

[2] For the three months and nine months ended September 30, 2013 and 2012, a refund was received for $4.1 million and $9.0 million, respectively, of Canadian taxes related to prior year tax returns. In addition, a refund was received for $3.1 million of United States taxes in the first half of 2013, related to prior year tax returns.

[3] Included capitalized interest, amortization of deferred financing costs and debt discounts.

[4] Excluded sale-leaseback capital leases.