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Interest Rate Caps - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Derivative [Line Items]    
Notional amount of interest rate cap $ 250,000,000  
Strike rate 2.50%  
London Interbank Offered Rate (LIBOR) [Member]    
Derivative [Line Items]    
Interest rate 1.56% 0.77%
Interest Rate Cap Contracts Expiring in April 2018 [Member]    
Derivative [Line Items]    
Notional amount of interest rate cap $ 150,000,000  
Maturity period of interest rate caps exchanged Apr. 30, 2018  
Interest Rate Cap Contracts Expiring in March 2019 [Member]    
Derivative [Line Items]    
Notional amount of interest rate cap $ 50,000,000  
Maturity period of interest rate caps exchanged Mar. 31, 2019  
Interest Rate Cap Contracts Expiring In June 2020 [Member]    
Derivative [Line Items]    
Notional amount of interest rate cap $ 50,000,000  
Maturity period of interest rate caps exchanged Jun. 30, 2020