Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Remaining Unfunded Commitments to Venture Capital or Private Equity Funds by our Consolidated Managed Funds (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Other Commitments [Line Items]
Unfunded Commitments	$ 5,849
Strategic Investors Fund, LP
Other Commitments [Line Items]
Unfunded Commitments	1,338
Capital Preferred Return Fund, LP
Other Commitments [Line Items]
Unfunded Commitments	1,936
Growth Partners, LP
Other Commitments [Line Items]
Unfunded Commitments	$ 2,575