Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Other Invested Assets [Line Items]
Other invested assets	$ 394,951	$ 377,429
Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	333,162	286,490
Company’s investment in separate accounts
Other Invested Assets [Line Items]
Other invested assets	43,497	40,126
Derivative Instruments
Other Invested Assets [Line Items]
Other invested assets	18,292	50,813
Equity Method | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	263,938	216,586
Equity Method | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	183,095	149,164
Equity Method | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	61,090	57,171
Equity Method | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	19,753	10,251
Fair Value | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	69,224	69,904
Fair Value | Private equity | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	57,156	60,118
Fair Value | Hedge funds | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	778	762
Fair Value | Real estate-related | Total LPs/LLCs
Other Invested Assets [Line Items]
Other invested assets	$ 11,290	$ 9,024