Annual report pursuant to Section 13 and 15(d)

Derivative Financial Instruments - Summary of Interest Rate Swap Agreement (Detail)

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Derivative Financial Instruments - Summary of Interest Rate Swap Agreement (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Mar. 31, 2016
Dec. 31, 2015
Derivative [Line Items]      
Notional Amount   $ 100,000,000 $ 50,000,000
Interest Rate Swap [Member]      
Derivative [Line Items]      
Notional Amount $ 100,000,000    
Effective Date Sep. 04, 2013    
Expiration Date Sep. 04, 2018    
Fixed Rate Paid 1.371%    
Interest Rate Swap [Member] | London Interbank Offered Rate (LIBOR) [Member]      
Derivative [Line Items]      
Floating Rate Received 1 month LIBOR