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Debt - Narrative (Details) - USD ($) |  |  |  | 3 Months Ended | 6 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Apr. 07, 2020 | Apr. 01, 2019 | Dec. 03, 2018 | Jun. 30, 2020 | Mar. 31, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019 | Dec. 23, 2019 | Mar. 31, 2019 | Dec. 31, 2018 | Jun. 15, 2018 | May 11, 2018
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | $ 2,656,900,000 |  | $ 2,483,000,000.0 | $ 2,656,900,000 | $ 2,483,000,000.0 | $ 2,746,000,000.0 |  |  | $ 2,328,700,000 |  |
Total debt |  |  |  | 349,800,000 |  |  | 349,800,000 |  | 283,500,000 |  |  |  |  |
Total commitment under revolving credit facility | $ 291.4 |  |  |  | $ 234,000,000.0 |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  | (1,100,000) | (21,700,000) |  |  |  |  |  |
NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 100,000,000.0
Other Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  | 16,300,000 |  |  | 16,300,000 |  |  |  |  |  |  |
NSM Holding Co LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | 268,400,000 |  |  | 268,400,000 |  | 219,200,000 |  |  |  |  |
NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | 267,000,000.0 |  |  | 267,000,000.0 |  | 217,400,000 |  |  |  |  |
Face amount |  |  |  | $ 273,400,000 | 220,700,000 | 222,300,000 | $ 273,400,000 | 222,300,000 | $ 221,300,000 |  | $ 186,400,000 | $ 180,400,000 |  |
Percentage of discounted future cash flows |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  |  | 7.21% |  |  | 7.21% |  | 6.60% |  |  |  |  |
Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  | $ 124,000,000.0 |  |  |  |
Kudu | Kudu Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | $ 70,800,000 |  |  | $ 70,800,000 |  | $ 53,600,000 |  |  |  |  |
Term Loan | Other Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  | 11,300,000 |  |  | 11,300,000 |  |  |  |  |  |  |
Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount | 276,400,000 |  |  | $ 273,400,000 | 224,000,000.0 |  | $ 273,400,000 |  | $ 221,300,000 |  |  |  |  |
Effective percentage |  |  |  | 7.20% |  |  | 7.20% |  | 7.50% |  |  |  |  |
Unamortized issuance cost |  |  |  | $ (6,400,000) |  |  | $ (6,400,000) |  | $ (3,900,000) |  |  |  |  |
Repayments of debt |  |  |  | 0 |  | (500,000) | (600,000) | (1,000,000.0) |  |  |  |  |  |
Proceeds from borrowings |  |  |  | 52,400,000 |  | 42,900,000 | 52,400,000 | 42,900,000 |  |  |  |  |  |
Debt Instrument, Increase (Decrease), Other, Net |  |  |  | 300,000 |  | 0 | 300,000 | 0 |  |  |  |  |  |
Term Loan | NSM Holding Co LLC | Other NSM |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | 1,400,000 |  |  | 1,400,000 |  | $ 1,800,000 |  |  |  |  |
Face amount |  |  |  | $ 1,600,000 |  |  | $ 1,600,000 |  |  |  |  |  |  |
Effective percentage |  |  |  | 3.20% |  |  | 3.20% |  | 3.00% |  |  |  |  |
Term Loan | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount |  |  |  | $ 74,000,000.0 |  |  | $ 74,000,000.0 |  | $ 57,000,000.0 |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  | 57,000,000.0 |  |  |  |
Proceeds from Issuance of Long-term Debt |  |  |  | $ 5,000,000.0 |  |  | $ 17,000,000.0 |  |  |  |  |  |  |
Term Loan | Kudu | Kudu Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Effective percentage |  |  |  | 8.10% |  |  | 8.10% |  | 8.30% |  |  |  |  |
Unamortized issuance cost |  |  |  | $ (3,200,000) |  |  | $ (3,200,000) |  | $ (3,400,000) |  |  |  |  |
Term Loan | Other | Other |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | 10,600,000 |  |  | 10,600,000 |  | 10,700,000 |  |  |  |  |
Face amount |  |  |  | $ 10,900,000 |  |  | $ 10,900,000 |  | $ 11,100,000 |  |  |  |  |
Effective percentage |  |  |  | 9.30% |  |  | 9.30% |  | 8.30% |  |  |  |  |
Unamortized issuance cost |  |  |  | $ (300,000) |  |  | $ (300,000) |  | $ (400,000) |  |  |  |  |
Delayed Draw Term Loans [Member] | Other Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  | 3,000,000.0 |  |  | 3,000,000.0 |  |  |  |  |  |  |
Delayed Draw Term Loans [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  | 62,000,000.0 |  |  |  |
Delayed Draw Term Loans [Member] | Kudu | Kudu Debt [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  | 125,000,000.0 |  |  |  |  |
Revolving Credit Facility | Other Operations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  | 2,000,000.0 |  |  | 2,000,000.0 |  |  |  |  |  |  |
Revolving Credit Facility | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility | 15,000,000.0 |  |  |  | $ 10,000,000.0 |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  | 0 |  | (6,500,000) | 0 | (6,500,000) |  |  |  |  |  |
Proceeds from borrowings |  |  |  | $ 0 |  | 0 | $ 0 | 6,500,000 |  |  |  |  |  |
Revolving Credit Facility | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  | $ 5,000,000.0 |  |  |  |
Interest Rate Swap | NSM Holding Co LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative, fixed interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 2.97% |
Derivative, variable interest rate |  |  |  | 0.17% |  |  | 0.17% |  |  |  |  |  |  |
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | $ 148,400,000 |  |  | $ 148,400,000 |  |  |  |  |  |  |
Total commitment under revolving credit facility |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
Hedged Liability, Fair Value Hedge |  |  |  |  |  |  |  |  |  |  |  |  | $ 151,000,000.0 |
Derivative, fixed interest rate |  |  |  |  | 2.97% |  |  |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  |  | 6.78% |  |  | 6.78% |  |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Increase (Decrease) |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 4.25% |  | 5.50% |  |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) | Minimum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 5.50% |  |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Increase (Decrease) |  |  |  |  |  |  | 1.25% |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  | 4.75% |  | 6.00% |  |  |  |  |  |  |
London Interbank Offered Rate (LIBOR) | Maximum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 6.25% |  |  |  |  |  |  |
Prime Rate | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 1.00% |  |  |  |  |  |  |
Prime Rate | Minimum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 4.50% |  |  |  |  |  |  |
Prime Rate | Maximum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 5.25% |  |  |  |  |  |  |
Designated as Hedging Instrument | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  |  | 6.67% |  |  | 6.67% |  |  |  |  |  |  |
Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | $ 148,400,000 |  |  | $ 148,400,000 |  |  |  |  |  |  |
Debt, weighted average interest rate, all-in |  |  |  | 8.72% |  |  | 8.72% |  |  |  |  |  |  |
Not Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | $ 125,000,000.0 |  |  | $ 125,000,000.0 |  |  |  |  |  |  |
Effective percentage |  |  |  | 6.90% |  |  | 6.90% |  |  |  |  |  |  |
Kingsbridge [Member] | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings |  |  |  | $ 52,400,000 |  |  |  |  |  |  |  |  |  |
Embrace | NSM Holding Co LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings |  | $ 20,400,000 |  |  |  |  |  |  |  |  |  |  |  |
Embrace | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings |  |  |  |  |  | $ 20,400,000 |  |  |  |  |  |  |  |
KBK Insurance Group, Inc. & KBK Premium Services, Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings |  |  | $ 30,100,000 |  |  |  |  |  |  |  |  |  |  |
Renewal Rights | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings |  |  |  |  |  |  |  | $ 22,500,000 |  |  |  |  |  |
Carrying Value | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total debt |  |  |  | 267,000,000.0 |  |  | $ 267,000,000.0 |  | 217,400,000 |  |  |  |  |
Debt securities issued by corporations |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | 505,800,000 |  |  | 505,800,000 |  | 467,200,000 |  |  |  |  |
Debt securities issued by corporations | AAA |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | 8,300,000 |  |  | 8,300,000 |  | 9,500,000 |  |  |  |  |
Debt securities issued by corporations | AA |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | 53,600,000 |  |  | 53,600,000 |  | 73,900,000 |  |  |  |  |
Debt securities issued by corporations | Standard & Poor's, A Rating [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | 314,100,000 |  |  | 314,100,000 |  | 288,500,000 |  |  |  |  |
Debt securities issued by corporations | BBB |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | 128,100,000 |  |  | 128,100,000 |  | 95,300,000 |  |  |  |  |
Debt securities issued by corporations | BB |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments |  |  |  | $ 1,700,000 |  |  | $ 1,700,000 |  | $ 0 |  |  |  |  |
United Kingdom, Pounds | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount | 42,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
United Kingdom, Pounds | London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 6.00% |  |  |  |  |  |  |
United Kingdom, Pounds | London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Increase (Decrease) |  |  |  |  |  |  | 1.25% |  |  |  |  |  |  |
Basis spread on variable rate |  |  |  |  |  |  | 6.50% |  |  |  |  |  |  |
Derivative, Cap Interest Rate |  |  |  | 1.25% |  |  | 1.25% |  |  |  |  |  |  |
United Kingdom, Pounds | Kingsbridge [Member] | NSM Holding Co LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings | 42,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |
United States of America, Dollars | Term Loan | NSM Holding Co LLC | NSM Bank Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Face amount | 52,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |
United States of America, Dollars | Kingsbridge [Member] | NSM Holding Co LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from borrowings | $ 52,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of increase (decrease) in debt instruments, classified as other. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(f)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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