GOODWILL AND INTANGIBLE ASSETS - Summary of Gross Amount and Accumulated Amortization by Category (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 515,388	$ 515,388
Accumulated amortization	(317,588)	(306,671)	$ (291,901)	$ (275,846)
Intangible Assets, Net (Excluding Goodwill), Total	197,800	208,717
U.S. state licenses
Finite-Lived Intangible Assets [Line Items]
Gross amount	26,036	26,036
Intangible Assets, Net (Excluding Goodwill), 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)
Intangible Assets, Net (Excluding Goodwill), Total	0	0
Novae | Coverholders
Finite-Lived Intangible Assets [Line Items]
Gross amount	63,565	63,565
Accumulated amortization	(27,812)	(22,514)
Intangible Assets, Net (Excluding Goodwill), Total	35,753	41,051
Novae | Large brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	46,641	46,641
Accumulated amortization	(16,325)	(13,215)
Intangible Assets, Net (Excluding Goodwill), Total	30,316	33,426
Novae | SME brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	14,126	14,126
Accumulated amortization	(6,180)	(5,003)
Intangible Assets, Net (Excluding Goodwill), Total	7,946	9,123
Novae | Syndicate capacity
Finite-Lived Intangible Assets [Line Items]
Gross amount	94,748	94,748
Intangible Assets, Net (Excluding Goodwill), 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	(10,329)	(8,997)
Intangible Assets, Net (Excluding Goodwill), Total	$ 3,001	$ 4,333