Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Other Invested Assets [Line Items]
Other invested assets	$ 462,257	$ 429,558
Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	385,746	370,437
Company’s investment in separate accounts
Other Invested Assets [Line Items]
Other invested assets	45,490	46,573
Derivative Instruments
Other Invested Assets [Line Items]
Other invested assets	31,021	12,548
Equity Method | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	306,227	295,529
Equity Method | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	200,106	189,095
Equity Method | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	61,950	64,002
Equity Method | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	44,171	42,432
Fair Value | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	79,519	74,908
Fair Value | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	66,644	62,639
Fair Value | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	551	562
Fair Value | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	$ 12,324	$ 11,707