Summary of Estimated Fair Values of Investments and Remaining Unfunded Commitments for Each Major Category of Investments (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	$ 836,725
Unfunded Commitments	398,525
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	611,824	[1]
Unfunded Commitments	309,765	[1]
Non-marketable securities | Equity method accounting | Other investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Fair Value	61,227	[2]
Unfunded Commitments	8,750	[2]
Estimated future period of distributions from the fund investments	10
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	163,674	[3]
Unfunded Commitments	80,010	[3]
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
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
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
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
Non-marketable securities | Noncontrolling Interest | 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	534,200
Unfunded Commitments	$ 296,400

[1] Venture capital and private equity fund investments within non-marketable securities (fair value accounting) include investments made by our managed funds of funds, one of our direct venture funds and one other private equity fund. These investments represent investments in venture capital and private equity funds that invest primarily in U.S. and global technology and life sciences companies. Included in the fair value and unfunded commitments of fund investments under fair value accounting are $534.2 million and $296.4 million, respectively, attributable to noncontrolling interests. It is estimated that we will receive distributions from the fund investments over the next 10 to 13 years, depending on the age of the funds and any potential extensions of terms of the funds.

[2] Other investments within non-marketable securities (equity method accounting) include investments in debt funds and venture capital and private equity fund investments that invest in or lend money to primarily U.S. and global technology and life sciences companies. It is estimated that we will receive distributions from the fund investments over the next 10 years, depending on the age of the funds.

[3] Venture capital and private equity fund investments within non-marketable securities (cost method accounting) include investments in venture capital and private equity fund investments that invest primarily in U.S. and global technology and life sciences companies. It is estimated that we will receive distributions from the fund investments over the next 10 to 13 years, depending on the age of the funds and any potential extensions of the terms of the funds.