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Financing Activities - Distributions (Details) - $ / shares
1 Months Ended 3 Months Ended
Feb. 28, 2018
Mar. 31, 2018
Mar. 31, 2017
Distributions (Numeric) [Abstract]      
Dividend payable date of quarterly common stock dividend Apr. 02, 2018    
Current quarterly common stock dividend (in dollars per share) $ 0.410 $ 0.41 $ 0.395
Annualized current quarterly common stock dividend (in dollars per share) $ 1.64