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STOCKHOLDERS' EQUITY - Summary of Restricted Stock, Restricted Stock Unit and Performance-based Stock Unit Activity (Detail)
$ / shares in Units, shares in Thousands, $ in Thousands
9 Months Ended
Sep. 30, 2019
USD ($)
$ / shares
shares
Restricted Stock, Restricted Stock Units And Performance Stock Units  
Restricted Stock, Restricted Stock Units, and Performance Stock Units  
Outstanding, beginning of period (in shares) 686
Granted (in shares) 163
Forfeited (in shares) (7)
Outstanding, end of period (in shares) 625
Weighted Average Grant Date Fair Value  
Outstanding at beginning of period (in dollars per share) | $ / shares $ 15.56
Granted (in dollars per share) | $ / shares 37.14
Forfeited (in dollars per share) | $ / shares 20.48
Outstanding at end of period (in dollars per share) | $ / shares $ 22.36
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value  
Contractual term at end of period 1 year 1 month 6 days
Aggregate intrinsic value at end of period | $ $ 12,866
Restricted Stock, Restricted Stock Units And Performance Stock Units | Class A Common Stock  
Restricted Stock, Restricted Stock Units, and Performance Stock Units  
Class A Common Stock Vested (in shares) (217)
Weighted Average Grant Date Fair Value  
Class A Common Stock Vested (in dollars per share) | $ / shares $ 12.19
Performance Stock Unit  
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value  
Percentage of attainment level 100.00%
Performance Stock Unit | Class A Common Stock  
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value  
Number of additional shares 325
Unvested | Restricted Stock, Restricted Stock Units And Performance Stock Units  
Restricted Stock, Restricted Stock Units, and Performance Stock Units  
Outstanding, end of period (in shares) 950
Weighted Average Grant Date Fair Value  
Outstanding at end of period (in dollars per share) | $ / shares $ 21.90
Weighted Average Remaining Contractual Term (years) and Aggregate Intrinsic Value  
Contractual term at end of period 1 year
Aggregate intrinsic value at end of period | $ $ 19,998