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Cash, Cash Equivalents, and Restricted Cash - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Restricted Cash And Cash Equivalents Items [Line Items]      
Restricted cash $ 10,425,000    
Investments 0 $ 0 $ 0
Realized gains or losses 0 0 0
Unrealized gains or losses 0 $ 0 $ 0
Held In Cash Money Market Account [Member]      
Restricted Cash And Cash Equivalents Items [Line Items]      
Restricted cash 10,000,000    
Held In Cash Collateral Accounts [Member]      
Restricted Cash And Cash Equivalents Items [Line Items]      
Restricted cash $ 425,000