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Stockholders' Equity - Additional Information (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended
Mar. 31, 2018
Dec. 31, 2017
Class of Stock [Line Items]    
Common stock, shares authorized (in shares) 450,000,000 450,000,000
Common stock, par value (in dollars per share) $ 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) 122,992,231 107,121,235
Common shares outstanding (in shares) 122,992,231 107,121,235
Proceeds from issuance of common stock, net of offering costs $ 275.9  
Series B Preferred Stock [Member]    
Class of Stock [Line Items]    
Preferred stock, shares issued (in shares) 6,770,393 6,770,393
Preferred stock, shares outstanding (in shares) 6,770,393 6,770,393
Preferred stock dividend percentage 8.00%  
Series C Preferred Stock [Member]    
Class of Stock [Line Items]    
Preferred stock, shares issued (in shares) 6,900,000 6,900,000
Preferred stock, shares outstanding (in shares) 6,900,000 6,900,000
Preferred stock dividend percentage 8.00%  
Common Stock [Member]    
Class of Stock [Line Items]    
Issuance of stock (in shares) 15,525,000  
Common Stock [Member] | Follow-on public offering [Member]    
Class of Stock [Line Items]    
Issuance of stock (in shares) 15,525,000  
Price per share of issued stock (in dollars per share) $ 17.77