Investments Limited Liability Investments (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Variable Interest Entity [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest		26.70%
Limited liability investments, at fair value	$ 31,416			$ 31,416		$ 32,211
Other than Temporary Impairment Losses, Investments	0		$ 0	0	$ 0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	200			200
Variable Interest Entity, Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 800			$ 800