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Equity-Based Compensation Plan - Summary of Performance Unit Award Activity (Detail) - Performance Shares [Member]
6 Months Ended
Jun. 30, 2017
shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]  
Outstanding at December 31, 2016 1,799,249
Granted 1,407,062
Settled 464,500
Forfeited (15,312)
Outstanding at June 30, 2017 2,726,499