Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Restricted Assets [Line Items]
Restricted assets	$ 9,330,777	$ 8,733,309
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	4,815,120	4,643,334
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	3,366,016	3,083,324
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	819,444	827,552
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	330,197	179,099
Watford Holdings Ltd
Restricted Assets [Line Items]
Assets pledged as collateral	$ 1,000,000	$ 954,600