Summary of Estimated Fair Values of Investments and Remaining Unfunded Commitments for Each Major Category of Investments (Textual) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	911,934
Unfunded Commitments	504,848
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	665,921
Unfunded Commitments	431,837
Non-marketable securities | Equity method accounting | Other investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	53,169
Unfunded Commitments	7,700
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	192,844
Unfunded Commitments	65,311
Non-marketable securities | Noncontrolling Interests | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	590,000
Unfunded Commitments	422,000
Non-marketable securities | Lower Limit | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	10 years
Non-marketable securities | Lower Limit | Equity method accounting | Other investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	10 years
Non-marketable securities | Lower Limit | Cost method accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	10 years
Non-marketable securities | Upper Limit | Fair value accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	13 years
Non-marketable securities | Upper Limit | Equity method accounting | Other investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	13 years
Non-marketable securities | Upper Limit | Cost method accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated future period of distributions from the fund investments	13 years