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Shareholders' Equity - Stock Buyback Program and Prospectus Supplement (Details) - USD ($)
9 Months Ended
Sep. 30, 2019
Jun. 12, 2019
Feb. 14, 2018
Nov. 09, 2017
Common shares | February 2018 Stock Buyback Program        
Equity, Class of Treasury Stock [Line Items]        
Stock repurchase program, authorized amount     $ 200,000,000  
Prospectus Supplement        
Equity, Class of Treasury Stock [Line Items]        
Maximum common stock value authorized under prospectus supplement       $ 150,000,000
Issuance of common stock under prospectus supplement (in shares) 0      
Amended Credit Agreement | Revolving Credit Facility | Line of Credit        
Equity, Class of Treasury Stock [Line Items]        
Maximum borrowing capacity   $ 900,000,000