Consolidated Company-Sponsored Investment Funds (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Gain (loss) on derivative instruments	$ 2,367	$ (9,492)
Cash collateral payable to trade counterparties	2,400		$ 500
Cash collateral received	4,700		8,800
Net assets of investment products that are non-consolidated VIEs	83,900,000
Maximum risk of loss in investment in VIEs	8,000
VIEs
Derivative [Line Items]
Futures, forwards and swaps held	12,600		8,400
Gain (loss) on derivative instruments	(14,900)	7,200
Cash collateral payable to trade counterparties	2,271		194
Cash collateral received	1,400		2,900
VOEs
Derivative [Line Items]
Futures, forwards and swaps held	38		300
Gain (loss) on derivative instruments	(500)	$ (400)
Cash collateral payable to trade counterparties	47		37
Cash collateral received	$ 300		$ 200