GOODWILL AND INTANGIBLE ASSETS - Summary of Gross Amount and Accumulated Amortization by Category (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 515,388	$ 515,388
Accumulated amortization	(339,421)	(328,505)	$ (317,588)	$ (306,671)
Total	175,967	186,883
U.S. state licenses
Finite-Lived Intangible Assets [Line Items]
Gross amount	26,036	26,036
Total	26,036	26,036
Novae | VOBA - Novae
Finite-Lived Intangible Assets [Line Items]
Gross amount	256,942	256,942
Accumulated amortization	(256,942)	(256,942)
Total	0	0
Novae | Coverholders
Finite-Lived Intangible Assets [Line Items]
Gross amount	63,565	63,565
Accumulated amortization	(38,408)	(33,110)
Total	25,157	30,455
Novae | Large brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	46,641	46,641
Accumulated amortization	(22,545)	(19,435)
Total	24,096	27,206
Novae | SME brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	14,126	14,126
Accumulated amortization	(8,533)	(7,357)
Total	5,593	6,769
Novae | Syndicate capacity
Finite-Lived Intangible Assets [Line Items]
Gross amount	94,748	94,748
Total	94,748	94,748
Tiernan | Customer relationships and customers lists - Ternian
Finite-Lived Intangible Assets [Line Items]
Gross amount	13,330	13,330
Accumulated amortization	(12,993)	(11,661)
Total	$ 337	$ 1,669