Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail)	12 Months Ended
	Dec. 31, 2015 USD ($) Investment	Dec. 31, 2014 USD ($) Investment	Dec. 31, 2013 USD ($) Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 107,886,000	$ 551,681,000	$ 455,531,000
Gross losses on investment securities	(18,441,000)	(284,658,000)	(36,123,000)
Gains on investment securities, net	89,445,000	267,023,000	419,408,000
Other than Temporary Impairment Losses, Investments	0	0	3,900,000
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 600,000	$ 800,000	$ 1,400,000
Number of other-than-temporary impaired investments | Investment	22	27	43
Number of investments | Investment	267	281	288
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 2,972,000	$ 658,000	$ 3,887,000
Gross losses on investment securities	(1,770,000)	(19,255,000)	(3,349,000)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	32,399,000	349,747,000	186,404,000
Gross losses on investment securities	(9,210,000)	(86,263,000)	(17,185,000)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	1,512,000	17,309,000	9,241,000
Gross losses on investment securities	(320,000)	(4,516,000)	(3,496,000)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	9,180,000	151,007,000	227,252,000
Gross losses on investment securities	(1,559,000)	(170,890,000)	(2,962,000)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	26,415,000	1,661,000	878,000
Gross losses on investment securities	(909,000)	(231,000)	(2,536,000)
Non-marketable securities | Equity method accounting | Debt Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	4,111,000	4,749,000	9,988,000
Gross losses on investment securities	(774,000)	(1,558,000)	(546,000)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,791,000	4,755,000	7,369,000
Gross losses on investment securities	(3,146,000)	(759,000)	(29,000)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	25,908,000	16,001,000	10,081,000
Gross losses on investment securities	(729,000)	(827,000)	(1,700,000)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	2,598,000	5,794,000	431,000
Gross losses on investment securities	$ (24,000)	$ (359,000)	$ (4,320,000)