XML 26 R109.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Stock Compensation Plans - Purchased Restricted Stock Plan - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
PRSUs [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Issued Shares (in shares) 61,991 66,674 41,801
Aggregate Purchase Price $ 8.5 $ 9.3 $ 5.8
Total fair value of vested $ 22.4    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Covered Shares (in shares) 30,996 33,337 20,901
Total fair value of vested $ 7.1    
Unrecognized compensation cost related to non-vested stock options and SSAR, RSU, PRS and Cash RSU awards granted $ 10.7    
Unrecognized compensation cost related to non-vested stock options and SSAR, RSU, PRS and Cash RSU awards granted, weighted average period, in years 1 year 9 months 18 days