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Derivatives - Narrative (Details) £ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 GBP (£)	Apr. 07, 2020 USD ($)	Dec. 31, 2018 USD ($)	May 18, 2018 USD ($)	May 11, 2018 USD ($)
Derivative [Line Items]
Total commitment under revolving credit facility				$ 291,400,000
Debt	$ 376,400,000	$ 283,500,000
NSM
Derivative [Line Items]
Debt	272,600,000	219,200,000
Long-term line of credit							$ 100,000,000.0
NSM Bank Facility | NSM
Derivative [Line Items]
Total commitment under revolving credit facility							234,000,000.0
Debt	277,400,000	221,300,000			$ 180,400,000
Long-term line of credit	277,400,000
NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility							$ 224,000,000.0
Debt	271,300,000	217,400,000
Long-term line of credit	$ 277,400,000	221,300,000		$ 276,400,000		$ 51,000,000.0
Interest Rate Swap | NSM
Derivative [Line Items]
Fixed interest rate	2.97%		2.97%
Variable interest rate	1.00%		1.00%
Net interest expense	$ 2,500,000	1,100,000
Derivative, fair value, net	8,200,000	6,600,000
Change in fair value of derivative instruments	$ (1,600,000)	$ (3,900,000)
Interest Rate Swap | NSM Bank Facility | NSM
Derivative [Line Items]
Debt, weighted average interest rate	8.40%		8.40%
Interest Rate Swap | NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility	$ 151,000,000.0
Debt	147,600,000
Interest Rate Cap | NSM
Derivative [Line Items]
Derivative, fair value, net	100,000
Change in fair value of derivative instruments	(100,000)
Premiums paid	$ 100,000
GBP-LIBOR rate	0.03%
Interest Rate Cap | NSM | London Interbank Offered Rate (LIBOR)
Derivative [Line Items]
Derivative, cap interest rate	1.25%		1.25%
Interest Rate Cap | NSM Bank Facility | NSM
Derivative [Line Items]
Debt instrument extension term (in years)	1 year
Interest Rate Cap | NSM Bank Facility | Term Loan
Derivative [Line Items]
Long-term line of credit	$ 52,400,000		£ 42.5
Designated as Hedging Instrument | NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Debt, weighted average interest rate	7.60%		7.60%
Designated as Hedging Instrument | Interest Rate Swap | NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Debt	$ 147,600,000
Debt, weighted average interest rate	9.00%		9.00%

X

- Definition

Face (par) amount of debt instrument at time of issuance.

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- Definition

Weighted average interest rate of debt outstanding.

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- Definition

Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

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The premium (cost) of a hedge, expensed during the period.

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- Definition

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

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Fixed interest rate related to the interest rate derivative.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Variable interest rate in effect as of the balance sheet date related to the interest rate derivative.

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- Definition

The net amount of operating interest income (expense).

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- Definition

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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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Debt Instrument, Term Extension

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LIBOR Rate

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