Fair Value Measurements - Fair Value of Certain Investments Based on NAV (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments	$ 1,078	$ 18,676
Equity Growth [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments	1,078	18,676
Equity Growth [Member] | Not Owned [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Unfunded commitments	$ 5,501	$ 6,888