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Stockholders' Equity - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Sep. 21, 2015
Dec. 31, 2016
Sep. 30, 2015
Mar. 31, 2015
Jun. 30, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Class of Stock [Line Items]                
Common stock, shares authorized (in shares)   450,000,000       450,000,000 450,000,000  
Common stock, par value (in dollars per share)   $ 0.01       $ 0.01 $ 0.01  
Preferred stock, shares authorized (in shares)   50,000,000       50,000,000    
Preferred stock, par value (in dollars per share)   $ 0.01       $ 0.01    
Common stock, shares issued (in shares)   91,422,676       91,422,676 67,195,252  
Common shares outstanding (in shares)   91,422,676       91,422,676 67,195,252  
Proceeds from issuance of common stock, net of offering costs   $ 177,796   $ 193,148 $ 158,439      
Payments of stock offering costs           $ 406 $ 987 $ 389
Repurchase of common stock           $ 0 $ 1,741 $ 0
Series A Preferred Stock [Member]                
Class of Stock [Line Items]                
Preferred stock dividend percentage           8.625%    
Preferred stock, shares issued (in shares)   3,450,000       3,450,000 3,450,000  
Preferred stock, shares outstanding (in shares)   3,450,000       3,450,000 3,450,000  
Series B Preferred Stock [Member]                
Class of Stock [Line Items]                
Preferred stock, shares issued (in shares)   8,000,000       8,000,000 8,000,000  
Preferred stock, shares outstanding (in shares)   8,000,000       8,000,000 8,000,000  
Series B Preferred Stock [Member] | Private Placement [Member]                
Class of Stock [Line Items]                
Issuance of stock (in shares) 8,000,000              
Price per share of issued stock (in dollars per share) $ 24.71              
Proceeds from private placement issuance $ 346,855              
Payments of stock offering costs $ 500              
Series C Preferred Stock [Member]                
Class of Stock [Line Items]                
Preferred stock dividend percentage           8.00%    
Preferred stock, shares issued (in shares)   6,900,000       6,900,000    
Preferred stock, shares outstanding (in shares)   6,900,000       6,900,000    
Common Stock [Member]                
Class of Stock [Line Items]                
Repurchases of common stock (in shares)     107,432       107,432  
Stock repurchases during period, price per share (in dollars per share)     $ 16.20          
Repurchase of common stock     $ 1,741          
Common Stock [Member] | Follow-on public offering [Member]                
Class of Stock [Line Items]                
Issuance of stock (in shares)   10,500,000   11,500,000 9,706,000      
Price per share of issued stock (in dollars per share)   $ 16.97   $ 16.82 $ 16.35 $ 16.97    
Common Stock [Member] | Private Placement [Member]                
Class of Stock [Line Items]                
Issuance of stock (in shares) 8,823,529              
Price per share of issued stock (in dollars per share) $ 17.00