Income Taxes - Deferred Tax Asset (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Financial Designation, Predecessor and Successor [Fixed List]	Successor	Successor	Successor	Predecessor	Successor	Successor	Predecessor
Investment in partnerships			$ 226,241		$ 226,241
Net operating losses		$ 6,810	1,753		1,753	$ 6,810
Tax Receivable Agreement			10,395		10,395
Employee compensation			9,888		9,888
Credits			8,342		8,342
Other		2,362	4,088		4,088	2,362
Deferred tax assets, gross		9,172	260,707		260,707	9,172
Total deferred tax assets, net		9,172	260,707		260,707	9,172
Deferred tax liabilities
Goodwill and Intangibles		(28,799)	(25,829)		(25,829)	(28,799)
Total deferred tax liabilities		(28,799)	(25,829)		(25,829)	(28,799)
Total deferred tax asset (liability)			$ 234,878		$ 234,878
Total deferred tax asset (liability)		$ (19,627)				$ (19,627)