Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Other Investments [Abstract]
Other invested assets	$ 1,915,297	$ 1,505,332
Limited Partner [Member]
Other Investments [Abstract]
Other invested assets	965,094	781,124
Gain (Loss) on Derivatives [Member]
Other Investments [Abstract]
Other invested assets	180,699	137,613
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Other Investments [Abstract]
Other invested assets	197,770	218,541
Other [Member]
Other Investments [Abstract]
Other invested assets	95,829	148,114
Equity Release Mortgages [Member]
Other Investments [Abstract]
Other invested assets	$ 475,905	$ 219,940