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Derivatives - Interest Rate Swap (Details) - USD ($)	3 Months Ended	8 Months Ended	12 Months Ended
Derivatives - Interest Rate Swap (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Jun. 15, 2018	May 11, 2018
Derivative [Line Items]
Debt	$ 283,500,000	$ 192,700,000	$ 283,500,000
NSM Holding Co LLC
Derivative [Line Items]
Debt	219,200,000	178,500,000	219,200,000
NSM Bank Facility \| NSM Holding Co LLC
Derivative [Line Items]
Total commitment under revolving credit facility					$ 234,000,000.0
NSM Bank Facility \| NSM Holding Co LLC \| Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility					$ 224,000,000.0
Debt	$ 217,400,000	$ 176,600,000	$ 217,400,000
NSM Bank Facility \| NSM Holding Co LLC \| Term Loan \| London Interbank Offered Rate (LIBOR) \| Minimum
Derivative [Line Items]
Basis spread on variable rate	4.25%	4.25%
NSM Bank Facility \| NSM Holding Co LLC \| Term Loan \| London Interbank Offered Rate (LIBOR) \| Maximum
Derivative [Line Items]
Basis spread on variable rate	4.75%	4.75%
NSM Bank Facility \| NSM Holding Co LLC \| Term Loan \| Prime Rate \| Minimum
Derivative [Line Items]
Basis spread on variable rate	3.25%	3.25%
NSM Bank Facility \| NSM Holding Co LLC \| Term Loan \| Prime Rate \| Maximum
Derivative [Line Items]
Basis spread on variable rate	3.75%	3.75%
Interest Rate Swap \| NSM Holding Co LLC
Derivative [Line Items]
Fixed interest rate	2.97%		2.97%
Variable interest rate	1.71%		1.71%
Net interest expense		$ 700,000	$ 1,100,000
Derivative, fair value, net	$ 6,600,000	2,700,000	6,600,000
Change in the fair value of the swap		$ (2,700,000)	$ (3,900,000)
Interest Rate Swap \| NSM Bank Facility \| NSM Holding Co LLC \| Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility				$ 151,000,000.0
Fixed interest rate	2.97%		2.97%
Debt	$ 148,700,000		$ 148,700,000
Debt, weighted average interest rate	7.06%		7.06%
Designated as Hedging Instrument \| Interest Rate Swap \| NSM Bank Facility \| NSM Holding Co LLC \| Term Loan
Derivative [Line Items]
Debt	$ 148,700,000		$ 148,700,000
Debt, weighted average interest rate	7.47%		7.47%