Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 20, 2020	Dec. 10, 2020 shares	Feb. 28, 2019 goal	Mar. 31, 2020	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized					$ 3.1	$ 4.5	$ 2.6
Stock-based compensation expense after tax					$ 2.5	$ 3.4	$ 2.0
Weighted-average fair value of options granted (in dollars per share) | $ / shares					$ 7.19	$ 10.26	$ 11.62
Aggregate intrinsic value of options exercised					$ 1.8	$ 12.3	$ 20.6
Total unrecognized compensation cost of nonvested stock options					$ 1.4
Expected weighted-average period					2 years 8 months 12 days
Non-Vested Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized					$ 0.6
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense recognized					$ 2.5
Vesting period				4 years	4 years
Weighted average fair value, granted (in dollars per share) | $ / shares					$ 37.52	$ 43.28	$ 48.38
Total compensation cost to be recognized					$ 6.7
Weighted average remaining contractual term					2 years 9 months 18 days
Total fair value, vested					$ 1.9	$ 1.5	$ 1.6
Granted (in shares) | shares					154,689
Executive Officers | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period			5 years
Number of goals | goal			3
Performance achievement period			3 years
Share-based Compensation Award, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted, vest in percentage per annum increments (as percent)					25.00%	25.00%	25.00%
Share-based Compensation Award, Tranche One | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance award vesting period					5 years
Share-based Compensation Award, Tranche One | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance award vesting period					7 years
Stock Incentive 2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants under 2018 Plan (in shares) | shares					1,500,000
Shares reserved for future issuance (in shares) | shares					504,931
Beneficial Acquisition Success Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Beneficial Acquisition Success Plan | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares) | shares		66,703