Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Other invested assets	$ 1,605,562	$ 1,505,332
Equity Release Mortgages [Member]
Other invested assets	311,723	219,940
Limited Partner [Member]
Other invested assets	857,599	781,124
Derivatives
Other invested assets	137,315	137,613
Fair Value Option Contractholder Directed Unit Linked Investments [Member]
Other invested assets	212,202	218,541
Other
Other invested assets	$ 86,723	$ 148,114