GOODWILL AND INTANGIBLE ASSETS - Gross amount and accumulated amortization by category (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross amount	$ 515,388	$ 515,388
Accumulated amortization	(306,671)	(291,901)
Total intangible assets	208,717	223,487
Customer relationships and customers lists - Ternian
Finite-Lived Intangible Assets [Line Items]
Gross amount	13,330	13,330
Accumulated amortization	(8,997)	(7,665)
Total intangible assets	4,333	5,665
Coverholders
Finite-Lived Intangible Assets [Line Items]
Gross amount	63,565	63,565
Accumulated amortization	(22,514)	(17,216)
Total intangible assets	41,051	46,349
Large brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	46,641	46,641
Accumulated amortization	(13,215)	(10,106)
Total intangible assets	33,426	36,535
SME brokers
Finite-Lived Intangible Assets [Line Items]
Gross amount	14,126	14,126
Accumulated amortization	(5,003)	(3,826)
Total intangible assets	9,123	10,300
U.S. state licenses
Finite-Lived Intangible Assets [Line Items]
Gross amount	26,036	26,036
Total intangible assets	26,036	26,036
Syndicate capacity
Finite-Lived Intangible Assets [Line Items]
Gross amount	94,748	94,748
Total intangible assets	94,748	94,748
Novae | VOBA - Novae
Finite-Lived Intangible Assets [Line Items]
Gross amount	256,942	256,942
Accumulated amortization	(256,942)	(253,088)
Total intangible assets	$ 0	$ 3,854