Quarterly report pursuant to Section 13 or 15(d)

Subsequent Events Subsequent Event, Series B Preferred Stock Offering (Details)

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Subsequent Events Subsequent Event, Series B Preferred Stock Offering (Details) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 6 Months Ended
Jul. 19, 2017
Jun. 30, 2017
Jun. 30, 2016
Dec. 31, 2016
Subsequent Event [Line Items]        
Preferred stock par value per share (in usd per share)   $ 0.01   $ 0.01
Proceeds from issuance of preferred stock, net of offering costs   $ 138,872 $ 0  
Series A Preferred Stock [Member]        
Subsequent Event [Line Items]        
Preferred stock dividend rate   8.125%    
Preferred stock par value per share (in usd per share)   $ 0.01    
Preferred stock public offering price per share (in usd per share)   25.00    
Preferred stock liquidation preference per share (in usd per share)   $ 25.00    
Preferred stock dividend variable rate spread   5.66%    
Preferred stock redemption price per share (in usd per share)   $ 25.00    
Proceeds from issuance of preferred stock, net of offering costs   $ 138,872    
Over-Allotment Option [Member] | Series A Preferred Stock [Member]        
Subsequent Event [Line Items]        
Number of shares of preferred stock issued during period (in shares)   750,000    
Subsequent Event [Member] | Series B Preferred Stock [Member]        
Subsequent Event [Line Items]        
Number of shares of preferred stock issued during period (in shares) 11,500,000      
Preferred stock dividend rate 7.625%      
Preferred stock par value per share (in usd per share) $ 0.01      
Preferred stock public offering price per share (in usd per share) 25.00      
Preferred stock liquidation preference per share (in usd per share) $ 25.00      
Preferred stock dividend variable rate spread 5.352%      
Preferred stock redemption price per share (in usd per share) $ 25.00      
Proceeds from issuance of preferred stock, net of offering costs $ 278,094      
Subsequent Event [Member] | Over-Allotment Option [Member] | Series B Preferred Stock [Member]        
Subsequent Event [Line Items]        
Number of shares of preferred stock issued during period (in shares) 1,500,000