Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Restricted Assets [Line Items]
Restricted assets	$ 7,811,500	$ 7,721,618
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	4,540,455	4,526,761
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	2,277,298	2,278,248
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	831,411	797,371
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	162,336	119,238
Watford Holdings Ltd
Restricted Assets [Line Items]
Assets pledged as collateral	$ 1,060,000	$ 1,000,000