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Shareholders' Equity - Prospectus Supplement (Details) - USD ($)
9 Months Ended 12 Months Ended
Mar. 13, 2017
Mar. 08, 2017
Mar. 07, 2017
Sep. 30, 2017
Dec. 31, 2016
Nov. 10, 2014
Class of Stock [Line Items]            
New issues (shares) 10,350,000   9,000,000      
Common stock, par value (in dollars per share)     $ 0.01 $ 0.01 $ 0.01  
Sale of stock, price per share (in dollars per share)     27.8      
Proceeds from issuance of common stock $ 288,100,000          
Over-Allotment Option            
Class of Stock [Line Items]            
Proceeds from issuance of common stock $ 37,600,000          
Prospectus Supplement            
Class of Stock [Line Items]            
New issues (shares)       0 0  
Maximum common stock value authorized under prospectus supplement           $ 150,000,000
Underwriters            
Class of Stock [Line Items]            
Sale of stock, price per share (in dollars per share)     $ 26.7      
Underwriters | Over-Allotment Option            
Class of Stock [Line Items]            
New issues (shares)   1,350,000        
Additional purchase of shares, exercise term     30 days