Investments (Other Invested Assets) (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Other Invested Assets [Line Items]
Other invested assets	[1]	$ 304,417	$ 263,074
Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		265,051	225,661
Company's investment in separate accounts
Other Invested Assets [Line Items]
Other invested assets		38,918	37,404
Derivatives
Other Invested Assets [Line Items]
Other invested assets		448	9
Equity Method Investments | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		202,934	184,063
Equity Method Investments | Private equity | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		138,775	123,957
Equity Method Investments | Hedge funds | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		53,480	53,066
Equity Method Investments | Real estate-related | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		10,679	7,040
Cost-method Investments
Other Invested Assets [Line Items]
Other invested assets			40,900
Fair Value | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		62,117	41,598
Fair Value | Private equity | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		54,836	35,686
Fair Value | Hedge funds | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		778	726
Fair Value | Real estate-related | Total LPS/LLCS
Other Invested Assets [Line Items]
Other invested assets		$ 6,503	$ 5,186

[1] Prior period amounts have been reclassified to conform to current period presentation. See "Adoption of ASU 2016-01" in Note 2 for details