Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Other invested assets	$ 2,006,870	$ 1,915,297
Limited Partner [Member]
Other invested assets	982,592	965,094
Equity Release Mortgages [Member]
Other invested assets	595,559	475,905
Derivatives
Other invested assets	132,412	180,699
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Other invested assets	202,848	197,770
Other
Other invested assets	$ 93,459	$ 95,829