XML 63 R53.htm IDEA: XBRL DOCUMENT v3.8.0.1
Stock-Based Compensation - Restricted Stock - Service-Based - Additional Information (Detail) - Service Based Restricted Stock [Member] - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Stock awards issued during the period 420,977  
Restricted shares vested grant date intrinsic value $ 0.8 $ 1.0
Unrecognized compensation expense $ 5.1  
Weighted average period 1 year 7 months 6 days  
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Grants vesting period 3 years