Income taxes: (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
Dec. 31, 2011	Dec. 31, 2012	Mar. 31, 2011
Income taxes:
Income Taxes, Foreign Statutory Corporate Tax Rate	26.50%	25.00%	28.00%
Difference in income tax provision from that calculated by applying the combined enacted Canadian federal and provincial statutory income tax rate
Loss before income taxes	$ (46,954)	$ (97,036)	$ (41,721)
Expected income tax recovery	12,443	24,259	11,682
Reduction (increase) in income taxes resulting from:
Non-deductible stock-based compensation	(1,642)	(3,019)	(1,379)
Other permanent differences	(87)	2,158	(600)
Withholding taxes	(500)	(1,187)	(303)
Change in enacted rates	(189)	(62)	24
Foreign tax rate differences, foreign exchange and other adjustments	552	382	(710)
Non-taxable income from equity investment	3,974	3,308	1,888
Change in valuation allowance	(13,391)	(27,577)	(11,023)
Total income tax recovery (expense)	$ 1,160	$ (1,738)	$ (421)

The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

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The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to changes in the valuation allowance for deferred tax assets in the period.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to changes in the income tax rates under enacted tax laws in the period.

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The portion of the difference between total income tax expense or benefit as reported in the income statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations that is attributable to withholding taxes.

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