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Stock Option Plans - Additional information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 15, 2018	Mar. 16, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2018
Stock Option Plans [Line Items]
Compensation expense related to stock option grants			$ 1.6	$ 4.4	$ 6.4	$ 8.5
Total intrinsic value of options exercised					33.4	$ 22.8
Total unrecognized compensation cost related to nonvested options			$ 39.7		$ 39.7
Weighted average period, years					4 years
Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum number of shares available					3,500,000
Shares available for grant			14,700,000		14,700,000
2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Number of years options expire from date of grant					7 years	7 years
Officer and Key Employees [Member] | 2017 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Shares available for grant	1,261,000		0	0	0	0
Stock options granted, exercise percentage, on the third anniversary date of the grant	34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant	33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant	33.00%
Officer and Key Employees [Member] | 2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Shares available for grant		1,650,400
Stock options granted, exercise percentage, on the third anniversary date of the grant		34.00%
Stock options granted, exercise percentage, on the fourth anniversary date of the grant		33.00%
Stock options granted, exercise percentage, on the fifth anniversary date of the grant		33.00%
Maximum [Member] | Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Maximum period for the exercise of stock options, years							7 years
Minimum [Member] | Long Term Incentive Plan [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%
Minimum [Member] | 2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Period of service from grant date stock options awarded not subject to forfeiture					2 years	2 years
Minimum [Member] | Executive Officer [Member] | 2014 Long Term Incentive Plan [Member]
Stock Option Plans [Line Items]
Minimum age of employee with not subject to award forfeiture on condition compliance					55 years	55 years
Black-Scholes Option Pricing Model [Member]
Stock Option Plans [Line Items]
Weighted average fair value per option for all options					$ 9.27	$ 11.42

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