Consolidated Company-Sponsored Investment Funds - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Cash collateral payable to trade counterparties	$ 500	$ 800
Cash collateral received	8,800	6,200
Net assets of investment products that are non-consolidated VIEs	53,600,000
Maximum risk of loss in investment in VIEs	7,900
VIEs [Member]
Derivative [Line Items]
Futures, forwards and swaps held	8,400	2,900
Gains (losses) on derivatives	21,500	800
Cash collateral payable to trade counterparties	194	461
Cash collateral received	2,900	$ 3,300
VOEs [Member]
Derivative [Line Items]
Futures, forwards and swaps held	300
Gains (losses) on derivatives	(400)
Cash collateral payable to trade counterparties	37
Cash collateral received	$ 200