Commitments, Contingencies and Guarantees (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Redeemable noncontrolling interests	$ 54,345	$ 62,886
Investment commitments	80
Amount of letters of credit outstanding	$ 5,248
Minimum
Other Commitments [Line Items]
Redeemable noncontrolling interest obligation, year of payment	2018
Maximum
Other Commitments [Line Items]
Redeemable noncontrolling interest obligation, year of payment	2023
Contractual redemption right
Other Commitments [Line Items]
Redemption value	$ 15,168
Contractual redemption right | Common Class A
Other Commitments [Line Items]
Redemption value	199
Termination or death redemption right
Other Commitments [Line Items]
Redemption value	33,470
Excess initial redemption value
Other Commitments [Line Items]
Redemption value	$ 5,705