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Subsequent Events - Dividend Announced (Details) - $ / shares
3 Months Ended 6 Months Ended
Jul. 31, 2018
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Subsequent Event [Line Items]          
Quarterly dividend per share (in usd per share)   $ 0.28 $ 0.24 $ 0.56 $ 0.48
Subsequent Event          
Subsequent Event [Line Items]          
Quarterly dividend per share (in usd per share) $ 0.28        
Declaration date Jul. 31, 2018        
Record date Aug. 24, 2018        
Payment date Sep. 14, 2018