Stock Option Plans - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2020	May 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Aug. 07, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant			3,449,686			3,000,000
Stock option expense			$ 4.9	$ 4.5	$ 3.8
Aggregate intrinsic value for outstanding options			35.8
Aggregate intrinsic value for exercisable options			18.8
Total intrinsic value of options exercised			26.4	2.2	2.1
Restricted stock or unit expense			$ 10.4	$ 15.3	$ 11.3
Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant						1,500,000
Performance Vesting Stock Options [Member] | Long Term Compensation Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant		96,476
Percentage of average return on invested capital			20.00%
Reduced percentage of shares earned in stock options plan			66.70%
Shares earned			96,476
Stock based compensation plan, description			The performance criterion for the Fiscal 2021 Employee Performance Stock Option Grant was based upon the achievement of certain levels of return on equity (as defined in the option agreements), ranging from 10.0% to 20.0%, for the fiscal year ending March 31, 2021. All stock options would be earned if the return on equity was 20.0% or greater, and the percentage of shares earned are reduced proportionately to approximately 66.7% if the return on equity was 10.0%. If the Company does not achieve a return on equity of at least 10.0%, all stock options granted would have been forfeited. During fiscal 2021, our adjusted return on equity was approximately 20.0%; therefore, all 96,476 options were earned.
Share-based compensation vesting period		4 years
Performance Vesting Stock Options [Member] | Long Term Compensation Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of average return on invested capital		10.00%
Share-based compensation expiration date			Mar. 31, 2022
Performance Vesting Stock Options [Member] | Long Term Compensation Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of average return on invested capital		20.00%
Share-based compensation expiration date			Mar. 31, 2024
Time Vesting Stock Options [Member] | Long Term Compensation Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant		80,396
Share-based compensation vesting period		4 years
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation cost, stock options			$ 7.0
Weighted-average period of recognition of unrecognized compensation cost			2 years 4 months 24 days
Stock Options [Member] | Long Term Compensation Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation award expiration term		10 years
Performance Vesting Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant		82,722
Percentage of average return on invested capital			20.00%
Shares earned			82,722
Stock based compensation plan, description			The performance criterion for the Fiscal 2020 Employee Restricted Stock Performance Award is based upon the achievement of certain levels of return on equity (as defined in the agreement), ranging from 10.0% to 20.0%, for the fiscal year ended March 31, 2021. All restricted shares would be earned if the return on equity was 20.0% or greater, and the percentage of shares earned will be reduced proportionately to approximately 66.7% if the return on equity was 10.0%. If the Company did not achieve a return on equity of at least 10.0%, all awards would have been be forfeited.
Share-based compensation vesting period		4 years
Reduced percentage of restricted shares			66.70%
Performance Vesting Restricted Stock [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of average return on invested capital		10.00%
Share-based compensation vesting date			Mar. 31, 2022
Performance Vesting Restricted Stock [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of average return on invested capital		20.00%
Share-based compensation vesting date			Mar. 31, 2024
Time Vesting Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant		68,936
Share-based compensation vesting period		4 years
Time Vesting Restricted Stock [Member] | Board of Director [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation vesting period		6 months
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant	26,064		267,000
Share-based compensation vesting period	6 months
Weighted-average period of recognition of unrecognized compensation cost			2 years 4 months 24 days
Unrecognized compensation cost			$ 12.6
Restricted Stock And Restricted Stock Unit [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for future grant			1,085,034