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Stockholders' Equity (Deficit) - Summary of Unvested Restricted Stock and Restricted Stock Unit (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares) (151,280) (607,231) (179,826)
Forfeited or expired (in shares) (86,518) (184,235) (89,699)
Restricted Stock Shares      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested at beginng of period (in shares) 1,045,416    
Shares issued (in shares) 571,438    
Vested (in shares) (296,754)    
Forfeited or expired (in shares) (91,542)    
Non-vested at end of period (in shares) 1,228,558 1,045,416  
Non-vested, Weighted- Average per Share Fair value on Grant Date, beginning of period (in usd per share) $ 45.21    
Fair value on grant date (in usd per share) 44.24    
Vested (in usd per share) 45.34    
Restricted stock forfeited or expired, Weighted- Average per Share Fair Value on Grant Date during the year 45.46    
Non-vested, Weighted- Average per Share Fair Value on Grant Date, end of period (in usd per share) $ 44.98 $ 45.21  
Aggregate Intrinsic Value $ 13.1    
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested at beginng of period (in shares) 557,422    
Shares issued (in shares) 219,923    
Vested (in shares) (151,280)    
Forfeited or expired (in shares) (64,122)    
Non-vested at end of period (in shares) 561,943 557,422  
Non-vested, Weighted- Average per Share Fair value on Grant Date, beginning of period (in usd per share) $ 45.34    
Fair value on grant date (in usd per share) 44.60    
Vested (in usd per share) 45.28    
Restricted stock forfeited or expired, Weighted- Average per Share Fair Value on Grant Date during the year 45.16    
Non-vested, Weighted- Average per Share Fair Value on Grant Date, end of period (in usd per share) $ 45.08 $ 45.34  
Aggregate Intrinsic Value $ 6.7