Consolidated Company-Sponsored Investment Funds - Offsetting of Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Derivative Asset [Abstract]
Cash Collateral Received	$ (500)	$ (800)
Variable Interest Entity, Primary Beneficiary [Member]
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	30,636	5,707
Gross Amounts Offset in the Statement of Financial Condition	0	0
Net Amounts of Assets Presented in the Statement of Financial Condition	30,636	5,707
Financial Instruments	0	0
Cash Collateral Received	(194)	(461)
Net Amount	30,442	5,246
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	22,241	2,791
Gross Amounts Offset in the Statement of Financial Condition	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	22,241	2,791
Financial Instruments	0	0
Cash Collateral Pledged	(2,884)	(2,791)
Net Amount	19,357	$ 0
VOEs [Member]
Derivative Asset [Abstract]
Gross Amounts of Recognized Assets	300
Gross Amounts Offset in the Statement of Financial Condition	0
Net Amounts of Assets Presented in the Statement of Financial Condition	300
Financial Instruments	0
Cash Collateral Received	(37)
Net Amount	263
Derivative Liability [Abstract]
Gross Amounts of Recognized Liabilities	631
Gross Amounts Offset in the Statement of Financial Condition	0
Net Amounts of Liabilities Presented in the Statement of Financial Condition	631
Financial Instruments	0
Cash Collateral Pledged	(228)
Net Amount	$ 403