Summary of Fair Value by Strategy Type Alongside Consolidated Funds of Hedge Funds' Remaining Unfunded Commitments and Ability to Redeem Such Investments (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2018
Diversified Instruments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments unable to be redeemed at, or within 3 months of reporting date	3.00%
Percentage of investments side pocketed as of reporting date	97.00%
Credit Driven
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments unable to be redeemed at, or within 3 months of reporting date	41.00%
Percentage of investments redeemable as of reporting date	59.00%
Equity
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments unable to be redeemed at, or within 3 months of reporting date	100.00%
Investee funds categorized as non redeemable, percentage	8.00%
Commodities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Percentage of investments unable to be redeemed at, or within 3 months of reporting date	100.00%