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Derivatives - NSM Interest Rate Swap (Details) - USD ($) $ in Millions	3 Months Ended		5 Months Ended	8 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 15, 2018
Derivative [Line Items]
Debt	$ 230.2			$ 192.7	$ 230.2
NSM Holding Co LLC
Derivative [Line Items]
Debt	219.4			178.5	219.4
NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Debt	217.7			176.6	217.7
Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Debt	$ 221.8				$ 221.8
Interest Rate Swap \| NSM Holding Co LLC
Derivative [Line Items]
Derivative, fixed interest rate							2.97%
Derivative, variable interest rate	2.11%				2.11%
Interest expense, net	$ 0.3		$ 0.3		$ 0.6	$ 0.4
Derivative, fair value, net	7.8			$ 2.7	7.8
Change in fair value of derivative	$ (0.8)	$ 1.0			$ (5.1)	$ (0.1)
Interest Rate Swap \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Total commitment under revolving credit facility							$ 151.0
Derivative, fixed interest rate	2.97%				2.97%
Debt	$ 149.1				$ 149.1
Debt, weighted average interest rate, all-in	7.17%				7.17%
Margin over London Interbank Offered Rate (LIBOR) \| Minimum \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	4.25%			4.25%
Margin over London Interbank Offered Rate (LIBOR) \| Maximum \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	4.75%			4.75%
Margin over Prime Rate \| Minimum \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	3.25%			3.25%
Margin over Prime Rate \| Maximum \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	3.75%			3.75%
Designated as Hedging Instrument \| Interest Rate Swap \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Debt	$ 149.1				$ 149.1
Debt, weighted average interest rate, all-in	7.47%				7.47%