Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) Investment	Mar. 31, 2015 USD ($) Investment		Dec. 31, 2015
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 10,389	$ 35,875
Gross losses on investment securities	(15,073)	(2,612)
(Losses) gains on investment securities, net	(4,684)	33,263	[1]
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 200	$ 100
Number of other-than-temporary impaired investments | Investment	10	9
Number of investments | Investment	267
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 1,753	$ 2,690
Gross losses on investment securities	(2,570)	(94)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,823	8,822
Gross losses on investment securities	(7,893)	(948)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	8	183
Gross losses on investment securities	(38)	(52)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	63	8,787
Gross losses on investment securities	(157)	(672)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	1,694	7,832
Gross losses on investment securities	(3,863)	(28)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	900	1,505
Gross losses on investment securities	(45)	(588)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	810	865
Gross losses on investment securities	(336)	0
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,338	4,833
Gross losses on investment securities	(171)	(224)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	0	358
Gross losses on investment securities	$ 0	$ (6)
Upper Limit
Gain (Loss) on Investments [Line Items]
Equity Method Investment Voting Ownership Percentage		27700.00%		5.00%

[1] Amounts for the three months ended March 31, 2015, have been revised to reflect the retrospective application of new accounting guidance adopted in the second quarter of 2015 related to our consolidated variable interest entities (ASU 2015-02).