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Stock Option Plans - Additional Information (Detail) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Aug. 31, 2015
Jun. 30, 2015
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Aug. 07, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of shares available for future grant     4,565,892     3,000,000
Stock option expense     $ 7.5 $ 6.2 $ 5.3  
Aggregate intrinsic value for outstanding options     31.0      
Aggregate intrinsic value of exercisable options     34.7      
Total intrinsic value of options exercised     6.7      
Restricted stock or unit expense     $ 9.8 $ 6.7 $ 4.8  
Maximum number of shares available for grant     1,439,758      
Stock Awards [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of shares available for future grant           1,500,000
Stock Options [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Unrecognized compensation cost, stock options     $ 8.1      
Weighted-average period of recognition of unrecognized compensation cost     2 years 3 months 18 days      
Stock Options [Member] | Long Term Compensation Plan [Member] | Employee [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of options, granted   268,571        
Share-based compensation vesting period   3 years        
Share-based compensation award expiration term   10 years        
Stock Options [Member] | Long Term Compensation Plan [Member] | Board of Directors [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of options, granted 17,051          
Share-based compensation award expiration term 10 years          
Restricted Stock [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Number of shares available for future grant 15,139 93,782        
Weighted-average period of recognition of unrecognized compensation cost     1 year 9 months 18 days      
Percentage of average return on invested capital     82.00%      
Shares earned     79,326      
Employee restricted stock award plan description     The performance criterion for the Fiscal 2016 Employee Restricted Stock Award is based upon the achievement of certain levels of return on equity, ranging from 12.5% to 17.5%, for the fiscal year ended March 31, 2016. All restricted shares will be earned if the return on equity is 17.5% or greater, and the percentage of shares earned will be reduced proportionately to approximately 75% if the return on equity is 12.5%. If the Company does not achieve a return on equity of at least 12.5%, all awards will be forfeited. If the criteria are met, the award may be reduced by the Compensation Committee based on individual performance goals.      
Reduced percentage of restricted shares   75.00%        
Remaining restrictions of unearned compensation cost     400,000      
Unrecognized compensation cost     $ 14.0      
Restricted Stock [Member] | Minimum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Share-based compensation vesting date     Mar. 31, 2017      
Percentage of average return on invested capital   12.50%        
Restricted Stock [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Share-based compensation vesting date     Mar. 31, 2020      
Percentage of average return on invested capital   17.50%        
Restricted Stock [Member] | Board of Directors [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Share-based compensation vesting period   5 years