Debt - Debt Outstanding (Details) € in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2021 EUR (€)	Jun. 02, 2021 USD ($)	Apr. 07, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument
Total debt	$ 693,000,000.0	$ 376,400,000
Weighted average interest rate	6.50%	7.00%
Ark Subordinated Notes
Debt Instrument
Unamortized issuance cost	$ (5,300,000)
Ark 2007 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	30,000,000.0
Ark 2007 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	0
Ark 2007 Notes | Ark Subordinated Notes
Debt Instrument
Total debt	30,000,000.0
Ark 2021 Notes Tranche 1
Debt Instrument
Long-term debt, gross | €			€ 39.1
Ark 2021 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	44,200,000
Ark 2021 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	47,000,000
Ark 2021 Notes Tranche 3 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	70,000,000.0
Ark 2021 Notes | Ark Subordinated Notes
Debt Instrument
Total debt	$ 155,900,000
Ark
Debt Instrument
Effective yield (as a percent)	6.90%		6.90%
Ark | Ark Subordinated Notes
Debt Instrument
Total debt	$ 185,900,000
NSM Bank Facility
Debt Instrument
Effective yield (as a percent)	8.20%	8.40%	8.20%
NSM
Debt Instrument
Total debt	$ 272,100,000	$ 272,600,000
NSM | NSM Bank Facility
Debt Instrument
Total debt	277,600,000	277,400,000				$ 221,300,000	$ 180,400,000
Debt instrument at face value	274,100,000
Kudu | Kudu Bank Facility
Debt Instrument
Total debt		86,300,000
Kudu | Kudu Credit Facility
Debt Instrument
Total debt	218,200,000
Other Operations | Other
Debt Instrument
Total debt	$ 16,800,000
Term Loan | Kudu Credit Facility
Debt Instrument
Effective yield (as a percent)	4.30%		4.30%
Term Loan | NSM | NSM Bank Facility
Debt Instrument
Total debt	$ 271,200,000	271,300,000
Unamortized issuance cost	(6,400,000)	(6,100,000)
Debt instrument at face value	$ 277,600,000	$ 277,400,000		$ 50,000,000	$ 276,400,000
Effective yield (as a percent)	7.30%	7.50%	7.30%
Term Loan | NSM | Other NSM
Debt Instrument
Total debt	$ 900,000	$ 1,300,000
Debt instrument at face value	$ 1,000,000
Effective yield (as a percent)	2.90%	2.50%	2.90%
Term Loan | Kudu | Kudu Bank Facility
Debt Instrument
Total debt	$ 0	$ 89,200,000				57,000,000.0	0
Unamortized issuance cost		(2,900,000)
Debt instrument at face value		$ 89,200,000
Effective yield (as a percent)		8.30%
Term Loan | Kudu | Kudu Credit Facility
Debt Instrument
Total debt	225,400,000	$ 0				$ 0	$ 0
Unamortized issuance cost	(7,200,000)
Debt instrument at face value	225,400,000
Term Loan | Other Operations | Other
Debt Instrument
Total debt		17,500,000
Unamortized issuance cost	(300,000)	(500,000)
Debt instrument at face value	$ 17,100,000	$ 18,000,000.0
Term Loan | Other Operations | Other Debt
Debt Instrument
Effective yield (as a percent)	7.50%	7.40%	7.50%