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Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 LLC Plan (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted, Weighted-average grant date fair value	$ 6.35
Plan 2015 | Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Number of Non-vested Units	0	971,906
Vested, Number of Units		(73,719)
Forfeited, Number of Units		(260,145)
Ending balance, Number of Non-vested Units		0
Vested or expected to vest, Number of Units		0
Beginning balance, Weighted-average price	$ 0	$ 5.22
Vested, Weighted-average price		4.01
Forfeited, Weighted-average price		4.19
Ending balance, Weighted-average price		0
Weighted-average price, Vested or expected to vest at December 31, 2017		0
Beginning Balance, Weighted-average grant date fair value	0	1.01
Vested, Weighted-average grant date fair value		0.87
Forfeited, Weighted-average grant date fair value		1.05
Ending balance, Weighted-average grant date fair value		0
Weighted-average grant date fair value, Vested or expected to vest at December 31, 2017		0
Plan 2015 | Incentive Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance, Weighted-average price	$ 0	5.93
Granted, Weighted-average price		0
Vested, Weighted-average price		5.53
Forfeited, Weighted-average price		5.57
Ending balance, Weighted-average price		0
Weighted-average price, Vested or expected to vest at December 31, 2017		$ 0
Plan 2015 | Incentive Units | 2017 Reorganization
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested units cancelled upon 2017 Reorganization, Number of Units		(638,042)
Non-vested units cancelled upon 2017 Reorganization, Weighted-average price		$ 5.78
Non-vested units cancelled upon 2017 Reorganization, Weighted-average grant date fair value		1.05
Plan 2015 | Incentive Units | 2017 Reorganization | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-vested units cancelled upon 2017 Reorganization, Weighted-average price		$ 6.15

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