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Stockholders' Equity - (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 1,100,000   1,100,000  
Stock-based compensation expense $ 3.8 $ 2.5 $ 6.9 $ 7.3
Share-based Payment Arrangement, Expense, Tax Benefit 1.0 0.6 1.8 1.9
Proceeds, Issuance of Shares, Share-based Payment Arrangement, Including Option Exercised     1.2 0.7
Payment, Tax Withholding, Share-based Payment Arrangement $ 0.0 $ 0.0 $ 1.7 $ 0.7
Weighted Average Number of Shares Outstanding, Diluted 16,971,000 16,783,000 16,689,000 16,689,000
Equity Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount $ 14.1   $ 14.1  
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of share-based awards granted     179,528  
Grant-date fair value of awards per share     $ 35.68  
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements 186,000 188,000 0 107,000
Performance Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of share-based awards granted     68,070  
Grant-date fair value of awards per share     $ 39.79  
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements 98,000 0 0 0