XML 72 R61.htm IDEA: XBRL DOCUMENT v3.19.2
Stock Option Plans - Additional information (Detail) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Mar. 14, 2019
Mar. 15, 2018
Jun. 30, 2019
Mar. 31, 2019
Jun. 30, 2018
Mar. 31, 2018
Jun. 30, 2019
Jun. 30, 2018
Stock Option Plans [Line Items]                
Maximum number of shares available       399,900   420,200    
Compensation expense related to stock option grants     $ 3.5 $ 3.6 $ 1.6 $ 4.8 $ 7.1 $ 6.4
Total intrinsic value of options exercised             48.3 $ 33.4
Total unrecognized compensation cost related to nonvested options     $ 36.4       $ 36.4  
Weighted average period, years             4 years  
Long Term Incentive Plan [Member]                
Stock Option Plans [Line Items]                
Maximum number of shares available             2,800,000  
Shares available for grant     13,100,000       13,100,000  
Number of years options expire from date of grant             7 years  
Officer and Key Employees [Member] | Long Term Incentive Plan [Member]                
Stock Option Plans [Line Items]                
Shares available for grant 1,283,300 1,261,000            
Stock options granted, exercise percentage, on the third anniversary date of the grant 34.00% 34.00%            
Stock options granted, exercise percentage, on the fourth anniversary date of the grant 33.00% 33.00%            
Stock options granted, exercise percentage, on the fifth anniversary date of the grant 33.00% 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 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%  
Period of service from grant date stock options awarded not subject to forfeiture             2 years 2 years
Minimum [Member] | Executive Officer [Member] | 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             $ 10.71 $ 9.27