Fair Value of Financial Instruments - Additional Information about Level 3 Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 123,427	$ 136,706	$ 117,989	$ 451,979
Total Realized and Unrealized Gains Included in Income	11,566	19,351	55,030	163,695
Purchases	0	6,304	0	22,800
Sales	(6,215)	(21,686)	(48,406)	(129,602)
Issuances	3,057	2,932	7,607	9,098
Distributions and Other Settlements	484	(102)	1,234	986
Transfers Out of Level 3	(486)	(6,245)	(1,621)	(381,696)
Ending Balance	131,833	137,260	131,833	137,260
Equity warrant assets | Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	120,037	87,151
Total Realized and Unrealized Gains Included in Income	11,551	13,805
Purchases	0	0
Sales	(6,215)	(10,564)
Issuances	3,057	2,932
Distributions and Other Settlements	499	510
Transfers Out of Level 3	(486)	(437)
Ending Balance	128,443	93,397	128,443	93,397
Non-marketable securities | Fair value accounting
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	3,390	49,555	3,291	352,088
Total Realized and Unrealized Gains Included in Income	15	5,546	146	112,370
Purchases	0	6,304	0	22,800
Sales	0	(11,122)	(32)	(62,401)
Issuances	0	0	0	0
Distributions and Other Settlements	(15)	(612)	(15)	(732)
Transfers Out of Level 3	0	(5,808)	0
Ending Balance	3,390	43,863	3,390	43,863
Non-marketable securities | Fair value accounting | Other venture capital investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	3,390	43,747
Total Realized and Unrealized Gains Included in Income	15	5,546
Purchases	0	6,304
Sales	0	(11,122)
Issuances	0	0
Distributions and Other Settlements	(15)	(612)
Transfers Out of Level 3	0	0		(380,262)
Ending Balance	$ 3,390	43,863	3,390	43,863
Non-marketable securities | Fair value accounting | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		5,808
Total Realized and Unrealized Gains Included in Income		0
Purchases		0
Sales		0
Issuances		0
Distributions and Other Settlements		0
Transfers Out of Level 3		(5,808)
Ending Balance		$ 0		0
Fair Value, Measurements, Recurring | Equity warrant assets | Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance			114,698	99,891
Total Realized and Unrealized Gains Included in Income			54,884	51,325
Purchases			0	0
Sales			(48,374)	(67,201)
Issuances			7,607	9,098
Distributions and Other Settlements			1,249	1,718
Transfers Out of Level 3			(1,621)	(1,434)
Fair Value, Measurements, Recurring | Non-marketable securities | Fair value accounting | Other venture capital investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance			3,291	32,839
Total Realized and Unrealized Gains Included in Income			146	8,060
Purchases			0	22,800
Sales			(32)	(15,561)
Issuances			0	0
Distributions and Other Settlements			(15)	(4,149)
Transfers Out of Level 3			$ 0	(126)
Fair Value, Measurements, Recurring | Non-marketable securities | Fair value accounting | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance				319,249
Total Realized and Unrealized Gains Included in Income				104,310
Purchases				0
Sales				(46,840)
Issuances				0
Distributions and Other Settlements				3,417
Transfers Out of Level 3				$ (380,136)