Annual report pursuant to Section 13 and 15(d)

Stock-based Expense - Awards Granted Assumptions (Detail)

v3.8.0.1
Stock-based Expense - Awards Granted Assumptions (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate     1.50%
Expected option life (in years)     4 years 7 months 6 days
Forfeiture rate     0.00%
Expected volatility     42.30%
Weighted-average grant date fair value (in dollars per share)     $ 7.42
Market Based Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.80% 1.10% 1.10%
Expected volatility 31.60% 41.50% 38.70%