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Subsequent Events - Additional Information (Detail) - USD ($)
3 Months Ended
Apr. 30, 2019
Apr. 04, 2019
Mar. 14, 2019
Mar. 31, 2019
Mar. 31, 2018
Apr. 01, 2019
Subsequent Event [Line Items]            
Dividend declared common share, per share     $ 0.13 $ 0.13 $ 0.15  
Series B Preferred Stock            
Subsequent Event [Line Items]            
Conversion of preferred stock, conversion rate (in shares)       5.2588    
Subsequent Event            
Subsequent Event [Line Items]            
Maximum amount of capital stock that may be offered per a registration statement   $ 490,236,182        
Purchases, Residential mortgage loans held-for-investment $ 74,500,000          
Subsequent Event | Series B Preferred Stock            
Subsequent Event [Line Items]            
Conversion of preferred stock, conversion rate (in shares)           5.3539