Amount of debentures that may be purchased by the underwriters per over-allotment option.

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Period of time allotted for purchase by underwriters of additional debentures.

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Amount of subordinated debt for which notice of intent to redeem has been provided.

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The portion of the carrying value of convertible subordinated debt as of the balance sheet date that is scheduled to be repaid after one year or beyond the normal operating cycle if longer. This form of debt can be exchanged for a specified amount of another security, typically the entity's common stock, at the option of the issuer or the holder, and places a lender in a lien position behind debt having a higher priority of repayment in liquidation of the entity's assets.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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The price per share of the conversion feature embedded in the debt instrument.

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Ratio applied to the conversion of debt instrument into equity with equity shares divided by debt principal amount.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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Convertible debentures (Details) $ / shares in Units, $ in Millions, $ in Millions				6 Months Ended
	Feb. 02, 2018 CAD ($)	Jan. 29, 2018 CAD ($)	Jan. 29, 2018 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 CAD ($)	Jun. 30, 2018 USD ($)	Jan. 29, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($)
Convertible debentures
Less: unamortized deferred financing costs						$ (4.7)		$ (1.6)
Less: Unamortized discount						(4.4)
Total convertible debentures						97.0		105.4
Net proceeds from issuance of convertible debentures, after underwriting discounts and expenses				$ 92.2
Derivative Liabilities measured at fair value						23.8		24.3
6.00% Debenture Due January 31, 2025
Convertible debentures
Long-term Debt, Gross						87.3
5.75% Debentures due June 2019
Convertible debentures
Long-term Debt, Gross								42.5
6.00% Debenture due December 2019
Convertible debentures
Long-term Debt, Gross						18.8		$ 64.5
Convertible Debentures
Convertible debentures
Less: unamortized deferred financing costs						(4.7)
Derivative Liabilities measured at fair value						$ 2.3	$ 4.7
Gain (loss) on derivatives			$ 0.0
Convertible Debentures \| 6.00% Debenture Due January 31, 2025
Convertible debentures
Long-term Debt, Gross					$ 115.0
Convertible debentures stated interest rate percentage					6.00%	6.00%
Convertible Debentures \| 5.75% Debentures due June 2019
Convertible debentures
Convertible debentures stated interest rate percentage					5.75%	5.75%
Notice to redeem remaining principal amount							$ 42.5
Convertible Debentures \| 6.00% Debenture due December 2019
Convertible debentures
Long-term Debt, Gross					$ 24.7
Convertible debentures stated interest rate percentage					6.00%	6.00%		6.00%
Notice to redeem remaining principal amount	$ 56.2
Convertible Unsecured Subordinated Debentures \| 6.00% Debenture due December 2019
Convertible debentures
Conversion rate of the debentures (in Shares per Dollar)		0.2380952	0.2380952
Conversion price of shares (in dollars per share) \| $ / shares							$ 4.20
Series E Debentures
Convertible debentures
Long-term Debt, Gross	15.0	$ 100.0
Net proceeds from issuance of convertible debentures, after underwriting discounts and expenses	$ 14.4	94.7
Series E Debentures \| Maximum
Convertible debentures
Amount of unerwriters option to purchase additional debentures		$ 15.0
Period of underwriters option to purchase		30 days	30 days