Investment Information - Restricted assets (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Restricted Assets [Line Items]
Restricted assets	$ 8,210,828	$ 7,721,618
Collateral or guarantees - affiliated transactions
Restricted Assets [Line Items]
Restricted assets	4,633,689	4,526,761
Collateral or guarantees - third party agreements
Restricted Assets [Line Items]
Restricted assets	2,525,173	2,278,248
Deposits with US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	862,859	797,371
Deposits with non-US regulatory authorities
Restricted Assets [Line Items]
Restricted assets	189,107	119,238
Watford Holdings Ltd
Restricted Assets [Line Items]
Assets pledged as collateral	$ 1,140,000	$ 1,000,000