Fair Value Measurements - Investments in Company-Sponsored Funds (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)
Investment Holdings [Line Items]
Fair Value	$ 7,632
Unfunded Commitments	$ 1,400
Hedge Funds [Member]
Investment Holdings [Line Items]
Investment Redemption Notice Period Minimum	30 days
Investment Redemption Notice Period Maximum	120 days
Fair Value	$ 2,624
Unfunded Commitments	$ 0
Redemption Frequency	Quarterly - Annually
Private Equity Funds
Investment Holdings [Line Items]
Investments Lock In Period	10 years
Fair Value	$ 5,008
Unfunded Commitments	$ 1,400