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Derivative Financial Instruments - Significant Assumptions Utilized in Binomial Lattice Process (Detail) - $ / shares
12 Months Ended
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2015
Dec. 01, 2014
Oct. 01, 2014
Aug. 14, 2014
Dec. 31, 2013
Derivative [Line Items]              
Linked common shares   130,208 130,208        
Quoted market price on valuation date $ 1.25   $ 2.50 $ 2.50 $ 2.50 $ 2.50 $ 2.50
Level 3 [Member] | Derivative Financial Instruments, Assets [Member]              
Derivative [Line Items]              
Linked common shares 130,208            
Quoted market price on valuation date $ 3.59            
Contractual exercise price $ 43.20            
Term (years) 7 months 6 days            
Level 3 [Member] | Minimum [Member] | Derivative Financial Instruments, Assets [Member]              
Derivative [Line Items]              
Range of market volatilities 29.90%            
Risk free rates using zero coupon US Treasury Security rates 0.20%            
Level 3 [Member] | Maximum [Member] | Derivative Financial Instruments, Assets [Member]              
Derivative [Line Items]              
Range of market volatilities 158.80%            
Risk free rates using zero coupon US Treasury Security rates 0.45%