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Note 25 - Subsequent Events (Details Textual) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Feb. 26, 2020
Jun. 30, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dividends, Common Stock, Total     $ 22,386 $ 26,834 $ 20,511
Common Stock, Dividends, Per Share, Declared     $ 0.44 $ 0.53 $ 0.44
AltaGas Power Holdings [Member] | Forecast [Member]          
Payments to Acquire Businesses, at Closing   $ 51,000      
AltaGas Power Holdings [Member] | Forecast [Member] | Maximum [Member]          
Payments to Acquire Businesses, Gross   $ 65,000      
Subsequent Event [Member]          
Dividends, Common Stock, Total $ 5,600        
Common Stock, Dividends, Per Share, Declared $ 0.11