Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation and Other Benefit Plans - Activity of Awarded Restricted Stock Units (Detail)

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Share-Based Compensation and Other Benefit Plans - Activity of Awarded Restricted Stock Units (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted Stock Units (RSUs)      
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value $ 3.0 $ 3.3 $ 0.8
Number of shares      
Balance at beginning of year (in shares) 208,040    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 13,175    
Vested (in shares) (74,888)    
Forfeited (in shares) (9,451)    
Balance at end of year (in shares) 136,876 208,040  
Weighted-Average Grant Date Fair Value      
Balance at beginning of year (in dollars per share) $ 47.35    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value 30.35    
Vested (in dollars per share) 39.40    
Forfeited (in dollars per share) 51.71    
Balance at end of year (in dollars per share) $ 49.76 $ 47.35  
Performance Restricted Stock Units [Domain]      
Number of shares      
Balance at beginning of year (in shares) 89,071    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period 15,066    
Vested (in shares) (3,917)    
Forfeited (in shares) (1,083)    
Balance at end of year (in shares) 79,914 89,071  
Weighted-Average Grant Date Fair Value      
Balance at beginning of year (in dollars per share) $ 58.69    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value 34.02    
Vested (in dollars per share) 63.25    
Forfeited (in dollars per share) 63.25    
Balance at end of year (in dollars per share) $ 52.73 $ 58.69  
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures and Expirations 19,223    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Intrinsic Value $ 62.92    
Minimum [Member] | Performance Restricted Stock Units [Domain]      
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Shares, Expected to Vest, Percentage 0.00%    
Maximum [Member] | Performance Restricted Stock Units [Domain]      
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Shares, Expected to Vest, Percentage 200.00%