Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity Preferred Stock Issuances (Details)

v3.8.0.1
Stockholders' Equity Preferred Stock Issuances (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 4,921 5,633  
Preferred stock par value per share (in usd per share) $ 0.01   $ 0.01
Proceeds from issuance of preferred stock, net of offering costs $ 13 $ 138,872  
Series A Preferred Stock [Member]      
Class of Stock [Line Items]      
Preferred stock dividend rate 8.125% 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    
Series A Preferred Stock [Member] | Public Offering [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 5,000,000    
Series A Preferred Stock [Member] | Over-Allotment Option [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 750,000    
Series B Preferred Stock [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 11,500,000    
Preferred stock dividend rate 7.625% 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    
Series B Preferred Stock [Member] | Over-Allotment Option [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 1,500,000    
Series C Preferred Stock [Member]      
Class of Stock [Line Items]      
Preferred stock dividend rate 7.25% 7.25%  
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 5.011%    
Preferred stock redemption price per share (in usd per share) $ 25.00    
Proceeds from issuance of preferred stock, net of offering costs $ 285,584    
Series C Preferred Stock [Member] | Public Offering [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 11,000,000    
Series C Preferred Stock [Member] | Over-Allotment Option [Member]      
Class of Stock [Line Items]      
Number of shares of preferred stock issued during period (in shares) 800,000