Investments Limited Liability Investments (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Limited liability investments	$ 5,316			$ 5,316		$ 9,094
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	200			200
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		26.70%
Alternative Investment	31,564			31,564		$ 32,211
Other than Temporary Impairment Losses, Investments	100		$ 0	100	$ 0
Variable Interest Entity, Primary Beneficiary [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 600			$ 600