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Stock-Based Compensation (Performance-Contingent Restricted Stock) - Additional Information (Detail) - Performance Contingent Restricted Stock
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized compensation cost related to nonvested restricted stock granted by the EPIP $ 10.7
Expected weighted-average period to recognize compensation cost (years) 1 year 11 days