Equity-based Awards - Summary of Restricted Stock Option Awards (Detail) - Restricted Stock Options [Member] - $ / shares		8 Months Ended	12 Months Ended
		Dec. 31, 2017	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Number of Options, Beginning Balance		614,754	517,398
Granted, Number of Options		1,876	0
Forfeited, Number of Options		(99,232)	(161,243)	[1]
Vested, Number of Options		0	(356,155)
Outstanding, Number of Options, Ending Balance		517,398	0
Outstanding, Weighted Average Grant Date Fair Value per Option, Beginning balance	[2]	$ 5.01	$ 5.01
Granted, Weighted-Average Grant Date Fair Value per Option	[2]	5.01	0
Forfeited, Weighted-Average Grant Date Fair Value per Option	[2]	5.01	5.01
Vested, Weighted-Average Grant Date Fair Value per Option	[2]	0	5.01
Outstanding, Weighted Average Grant Date Fair Value per Option, Ending balance	[2]	$ 5.01	$ 0

[1] In connection with certain grants awarded in 2018 pursuant to the Legacy Amplify MIP, all remaining unvested restricted stock options were forfeited.

[2] Determined by dividing the aggregate grant date fair value of awards by the number of awards issued.