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Class A Redeemable Convertible Preferred Stock (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Dec. 22, 2016
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 29, 2016
Dec. 30, 2015
Temporary Equity [Line Items]            
Temporary equity, shares issued   6,864,000   6,864,000    
Temporary equity, face value (in dollars per share)   $ 0.001   $ 0.001    
Temporary equity, shares outstanding   6,864,000   6,864,000    
Series A Redeemable Convertible Preferred Stock            
Temporary Equity [Line Items]            
Temporary equity, shares issued           14,666,667
Temporary equity, face value (in dollars per share) $ 7.50         $ 7.50
Temporary equity, liquidation value $ 49.5         $ 110.0
Temporary equity liquidation amount at redemption         $ 100.0  
Temporary equity shares redemption 8,066,667          
Temporary equity redemption amount $ 55.0          
Temporary equity, redemption per share (in dollars per share) $ 6.82          
Redemption discounts percentage 9.09%          
Temporary equity, shares outstanding   6,864,000        
Temporary equity, carrying amount   $ 35.5   $ 32.6    
Temporary equity, accrual of deemed dividends   0.8        
Temporary equity accretion of beneficial conversion feature   1.9        
Temporary equity, fair value $ 32.9         $ 73.2
Temporary equity issued, price per share (in dollars per share) $ 4.99         $ 4.99
Temporary equity issue discount $ 16.6         $ 36.8
Temporary equity, value of beneficial conversion feature $ 20.1         $ 44.7
Temporary equity, recognized amount of beneficial conversion feature   1.9        
Series A Redeemable Convertible Preferred Stock | Payment In Kind Period Two            
Temporary Equity [Line Items]            
Temporary equity, shares issued       264,000    
Temporary equity additional beneficial conversion feature discount value   0.2        
Temporary equity, fair value   $ 49.5        
Series A Redeemable Convertible Preferred Stock | Payment In Kind Period Two | Scenario, Forecast            
Temporary Equity [Line Items]            
Temporary equity, face value (in dollars per share)     $ 7.50      
Temporary equity, fair value     $ 49.5      
Additional preferred stock to be issued as paid in kind dividends     274,560      
Payment-in-kind dividend rate per annum in effect     4.00%