Fair Value (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) acquisition	Dec. 31, 2016 USD ($) acquisition
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments, Measurements Other than Fair Value	$ 100,606	$ 118,149
Investments, NAV Expedient	39,900
Assets measured at fair value for impairment on a nonrecurring basis	0	0
Liabilities measured at fair value for impairment on a nonrecurring basis	$ 0	$ 0
Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of acquisitions | acquisition	3	3
Private Equity Investment Energy Fund
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 4,900	$ 4,900
Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments, NAV Expedient	40,016	40,413
Contingent payment arrangements	16,777	17,589
Recurring | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent payment arrangements	$ 16,800	17,600
Weighted Average | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
AUM growth rate	18.00%
Minimum | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Revenue growth rate	4.00%
Discount rate	1.40%
Maximum | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Revenue growth rate	31.00%
Discount rate	6.40%
Level 3 | Recurring
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investments	$ 5,028	5,023
Contingent payment arrangements	16,777	$ 17,589
Private equity
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Unfunded commitment	$ 800