RESERVE FOR LOSSES AND LOSS EXPENSES - Reserve for losses and loss expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance Loss Reserves [Abstract]
Reserve for reported losses and loss expenses	$ 5,539,971	$ 5,331,900
Reserve for losses incurred but not reported	9,113,123	8,594,866
Reserve for losses and loss expenses	$ 14,653,094	$ 13,926,766	$ 12,752,081	$ 12,280,769