Basic and diluted earnings (loss) per share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Numerator:
Net income (loss) attributable to Atlantic Power Corporation	$ (42,292)	$ 6,136
Denominator:
Weighted average basic shares outstanding	113,578	67,654
Dilutive potential shares:
Convertible debentures (in shares)	13,252	14,809
LTIP notional units (in shares)	478	517
Potentially dilutive shares	113,578	68,171
Diluted EPS (in dollars per share)	$ (0.37)	$ 0.09

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References+ Details

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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+ Details

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References+ Details

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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+ Details