Quarterly report pursuant to Section 13 or 15(d)

Equity (Details)

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Equity (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended
Jun. 27, 2017
Jan. 21, 2017
Dec. 31, 2016
Sep. 30, 2017
Sep. 30, 2016
Class of Stock [Line Items]          
Redemption of preferred shares (6,900,000 shares)       $ 172,500  
Conversion of common units to common shares (in units/shares)       337,000 87,000
Common Stock Issued to Public Under At-the-Market Program          
Class of Stock [Line Items]          
Shares issued to the public (in shares)       591,042  
Issuance of stock, weighted average price per share (in dollars per share)       $ 33.84  
Net proceeds from shares issued       $ 19,700  
Payments of stock issuance costs       300  
At-market stock, offering program established, remaining capacity       70,000  
Series K Cumulative Preferred Stock          
Class of Stock [Line Items]          
Dividend rate (percent)   5.60%      
Preferred stock, redemption price per share (in dollars per share)   $ 50.00      
Redemption of preferred shares (6,900,000 shares)   $ 26,600      
Issuance costs associated with redeemed preferred shares     $ 17    
Series L Cumulative Preferred Stock          
Class of Stock [Line Items]          
Dividend rate (percent) 7.375%        
Preferred stock, redemption price per share (in dollars per share) $ 25.00        
Redemption of preferred shares (6,900,000 shares) $ 172,500        
Issuance costs associated with redeemed preferred shares       $ 6,800