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Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - USD ($)
$ / shares in Units, $ in Millions
May 06, 2019
Apr. 19, 2019
Apr. 08, 2019
Secured Loan Arrangements [Member] | 3.77% [Member]      
Subsequent Event [Line Items]      
Debt instrument gross amount     $ 15.0
Stated interest rate     3.77%
Debt maturity year     Apr. 08, 2023
Secured Loan Arrangements [Member] | 3.89% [Member]      
Subsequent Event [Line Items]      
Debt instrument gross amount   $ 10.0  
Stated interest rate   3.89%  
Debt maturity year   Apr. 19, 2023  
Class A Common Stock [Member]      
Subsequent Event [Line Items]      
Dividend declared per share $ 0.14    
Dividend payable declared date May 06, 2019    
Dividend payable, date to be paid Jun. 10, 2019    
Dividend payable record date May 24, 2019    
Class B Common Stock [Member]      
Subsequent Event [Line Items]      
Dividend declared per share $ 0.14    
Dividend payable declared date May 06, 2019    
Dividend payable, date to be paid Jun. 10, 2019    
Dividend payable record date May 24, 2019