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Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Mar. 12, 2020	Mar. 14, 2019	Mar. 15, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Option Plans [Line Items]
Compensation expense related to stock option grants				$ 13.6	$ 14.0	$ 13.7
Total intrinsic value of options exercised				106.4	$ 54.2	$ 77.9
Total unrecognized compensation cost related to nonvested options				$ 28.3
Weighted average period, years				4 years
Black-Scholes Option Pricing Model [Member]
Stock Option Plans [Line Items]
Weighted average fair value per option for all options				$ 9.99	$ 10.71	$ 9.27
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum number of shares available				2,300,000
Shares available for grant				11,400,000
Long Term Incentive Plan [Member] | Maximum [Member]
Stock Option Plans [Line Items]
Minimum exercise price of stock options, percent of fair market value of a share of common stock on the date of grant				100.00%
Maximum period for the exercise of stock options, years				7 years	7 years	7 years
Long Term Incentive Plan [Member] | Minimum [Member]
Stock Option Plans [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture				2 years	2 years	2 years
Long Term Incentive Plan [Member] | Minimum [Member] | Executive Officer [Member]
Stock Option Plans [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance				55 years	55 years	55 years
2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Number Of Periods Options Expire				7 years
2017 Long Term Incentive Plan [Member] | Officer and Key Employees [Member]
Stock Option Plans [Line Items]
Shares available for grant	1,590,740	1,283,300	1,261,000
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%	34.00%	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%	33.00%	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%	33.00%	33.00%

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