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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% |  |

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