Remaining Unfunded Commitments to Venture Capital or Private Equity Funds by our Consolidated Managed Funds (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Line Items]
Unfunded Commitments	$ 5,842
Strategic Investors Fund, L.P.
Commitments and Contingencies Disclosure [Line Items]
Unfunded Commitments	1,338
Capital Preferred Return Fund, L.P.
Commitments and Contingencies Disclosure [Line Items]
Unfunded Commitments	1,952
Growth Partners, L.P.
Commitments and Contingencies Disclosure [Line Items]
Unfunded Commitments	$ 2,552
Venture capital and private equity fund investments
Commitments and Contingencies Disclosure [Line Items]
Commitments Expiration Period	10 years
Fund Commitments, Call Unrestricted, Percentage of Committed Capital	100.00%
Lower Limit | Venture capital and private equity fund investments
Commitments and Contingencies Disclosure [Line Items]
Expected commitment period to invest in venture capital and private equity funds (in years)	5 years
Upper Limit | Venture capital and private equity fund investments
Commitments and Contingencies Disclosure [Line Items]
Expected commitment period to invest in venture capital and private equity funds (in years)	7 years