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Represents the number of power plants acquired.

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In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Note 12 - Subsequent Events (Details) (USD $)	3 Months Ended		0 Months Ended
Note 12 - Subsequent Events (Details) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Apr. 30, 2015	May 06, 2015
Note 12 - Subsequent Events (Details) [Line Items]
Dividends, Common Stock	$ 3,898,000us-gaap_DividendsCommonStock	$ 2,727,000us-gaap_DividendsCommonStock
Common Stock, Dividends, Per Share, Declared	$ 0.08	$ 0.06
Subsequent Event [Member] \| Northleaf Geothermal Holdings (Northleaf) [Member] \| Class B Membership Interests [Member]
Note 12 - Subsequent Events (Details) [Line Items]
Sale of Stock, Percentage of Ownership after Transaction			100.00%
Subsequent Event [Member] \| Northleaf Geothermal Holdings (Northleaf) [Member]
Note 12 - Subsequent Events (Details) [Line Items]
Equity Method Investment, Ownership Percentage			36.75%
Number of Power Plants Acquired			9
Business Combination, Consideration Transferred			162,300,000
Business Combination, Bargain Purchase, Gain Recognized, Amount			104,000,000
Subsequent Event [Member]
Note 12 - Subsequent Events (Details) [Line Items]
Dividends, Common Stock				$ 2,900,000
Common Stock, Dividends, Per Share, Declared				$ 0.06