Fair Value of Financial Instruments Summary of Estimated Fair Values of Investments and Remaining Unfunded Commitments for Each Major Category of Investments (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	$ 403,207
Fair Value	517,036
Unfunded Commitments	23,525
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]
Carrying Amount	152,237
Fair Value	152,237
Unfunded Commitments	7,049
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	85,705
Fair Value	85,705
Unfunded Commitments	4,954
Non-marketable securities | Equity method accounting | Debt Securities
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	21,970
Fair Value	23,080
Unfunded Commitments	0
Non-marketable securities | Equity method accounting | Other investments
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying Amount	22,619
Fair Value	22,619
Unfunded Commitments	886
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]
Carrying Amount	120,676
Fair Value	233,395
Unfunded Commitments	$ 10,636