Investment Securities - Components of Gains and Losses (Realized and Unrealized) on Investment Securities (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) Investment	Sep. 30, 2015 USD ($) Investment	Sep. 30, 2016 USD ($) Investment	Sep. 30, 2015 USD ($) Investment	Dec. 31, 2015 Investment
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 26,328	$ 21,787	$ 67,752	$ 85,175
Gross losses on investment securities	(3,150)	(3,019)	(25,988)	(8,169)
Gains on investment securities, net	23,178	18,768	41,764	77,006
Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Recognized other-than-temporary impairment (OTTI) losses	$ 100	$ 100	$ 500	$ 400
Number of other-than-temporary impaired investments | Investment	5	4	21	19
Number of investments | Investment	255	270	255	270	267
Available-for-sale Securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	$ 84	$ 46	$ 14,238	$ 2,971
Gross losses on investment securities	(99)	(33)	(2,671)	(221)
Non-marketable securities | Fair value accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,030	6,746	16,377	24,767
Gross losses on investment securities	(2,122)	(1,148)	(15,958)	(2,695)
Non-marketable securities | Fair value accounting | Other venture capital investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	4	15	17	198
Gross losses on investment securities	0	0	(38)	(52)
Non-marketable securities | Fair value accounting | Other securities
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	271	40	639	9,108
Gross losses on investment securities	(100)	(325)	(507)	(1,117)
Non-marketable securities | Equity method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	5,679	6,655	9,351	19,378
Gross losses on investment securities	(444)	(472)	(4,465)	(909)
Non-marketable securities | Equity method accounting | Debt funds
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	295	379	1,259	2,067
Gross losses on investment securities	(129)	(1)	(458)	(589)
Non-marketable securities | Equity method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	7,487	2,282	11,528	5,009
Gross losses on investment securities	(205)	(902)	(1,161)	(2,042)
Non-marketable securities | Cost method accounting | Venture capital and private equity fund investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	6,328	5,624	14,180	21,101
Gross losses on investment securities	(51)	(132)	(492)	(530)
Non-marketable securities | Cost method accounting | Other investments
Gain (Loss) on Investments [Line Items]
Gross gains on investment securities	150	0	163	576
Gross losses on investment securities	$ 0	$ (6)	$ (238)	$ (14)