Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Other Invested Assets [Line Items]
Other invested assets	$ 468,005	$ 429,558
Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	387,648	370,437
Company’s investment in separate accounts
Other Invested Assets [Line Items]
Other invested assets	44,685	46,573
Derivative Instruments
Other Invested Assets [Line Items]
Other invested assets	35,672	12,548
Equity Method | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	316,770	295,529
Equity Method | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	203,599	189,095
Equity Method | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	68,132	64,002
Equity Method | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	45,039	42,432
Fair Value | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	70,878	74,908
Fair Value | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	58,562	62,639
Fair Value | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	503	562
Fair Value | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	$ 11,813	$ 11,707