Fair Value (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($) investment acquisition	Dec. 31, 2016 USD ($) investment acquisition
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Number of private equity investments measured using practical expedient | investment	1	1
Private equity investments measured at cost	$ 39,500	$ 40,400
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]
Contingent payment arrangements	17,177	17,589
Recurring | Contingent Payment Arrangements
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Contingent payment arrangements	$ 17,200	$ 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%