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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Derivatives - NSM Interest Rate Swap (Details) - USD ($)	3 Months Ended	8 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Jun. 15, 2018	May 18, 2018	May 11, 2018
Derivative [Line Items]
Debt	$ 195,400,000	$ 192,700,000
NSM Holding Co LLC
Derivative [Line Items]
Debt	184,500,000	178,500,000
NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Debt	182,800,000	176,600,000
Face amount					$ 100,000,000.0
Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Debt	179,900,000
Face amount	$ 186,400,000	180,400,000		$ 51,000,000.0	$ 181,100,000
Interest Rate Swap \| NSM Holding Co LLC
Derivative [Line Items]
Derivative, fixed interest rate			2.97%
Derivative, variable interest rate	2.49%
Interest expense, net	$ 200,000
Derivative, fair value, net	4,600,000	$ 2,700,000
Change in fair value of derivative	$ (1,900,000)
Interest Rate Swap \| Term Loan \| NSM Bank Facility
Derivative [Line Items]
Derivative, variable interest rate	2.49%
Interest Rate Swap \| Term Loan \| NSM Holding Co LLC \| NSM Bank Facility
Derivative [Line Items]
Derivative, fixed interest rate	2.97%
Debt	$ 149,900,000
Total commitment under revolving credit facility			$ 151,000,000.0
Debt, weighted average interest rate, all-in	7.44%
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	$ 149,900,000
Debt, weighted average interest rate, all-in	7.47%