Fair Value of Financial Instruments Additional Information about Level 3 Assets Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity warrant assets | Other Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 135,168	$ 114,698
Total Realized and Unrealized Gains (Losses) Included in Income	38,091	71,402
Purchases	0	0
Sales	(56,643)	(61,044)
Issuances	13,405	12,534
Distributions and Other Settlements	0	0
Transfers Out of Level 3	(1,208)	(2,422)
Ending Balance		135,168	$ 114,698
Non-marketable securities | Fair value accounting | Other venture capital investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total Realized and Unrealized Gains (Losses) Included in Income		1,192
Purchases		0
Sales		(2,356)
Issuances		0
Distributions and Other Settlements		(87)
Transfers Out of Level 3		0
Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	137,208	185,902	451,979
Total Realized and Unrealized Gains (Losses) Included in Income	38,070	72,594	188,173
Purchases	0	0	51,407
Sales	(56,647)	(63,400)	(138,077)
Issuances	13,405	12,534	15,886
Distributions and Other Settlements	25	(87)	(1,484)
Transfers Out of Level 3	(1,208)	(2,422)	(381,982)
Ending Balance	130,853	137,208	185,902
Fair Value, Measurements, Recurring | Equity warrant assets | Other Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	135,168	114,698	99,891
Total Realized and Unrealized Gains (Losses) Included in Income			71,516
Purchases			0
Sales			(70,875)
Issuances			15,886
Distributions and Other Settlements			0
Transfers Out of Level 3			(1,720)
Ending Balance	128,813	135,168	114,698
Fair Value, Measurements, Recurring | Non-marketable securities | Fair value accounting
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		71,204	352,088
Total Realized and Unrealized Gains (Losses) Included in Income			116,657
Purchases			51,407
Sales			(67,202)
Issuances			0
Distributions and Other Settlements			(1,484)
Transfers Out of Level 3			(380,262)
Ending Balance			71,204
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	2,040	71,204	32,839
Total Realized and Unrealized Gains (Losses) Included in Income	(21)		12,793
Purchases	0		51,407
Sales	(4)		(20,362)
Issuances	0		0
Distributions and Other Settlements	25		(5,347)
Transfers Out of Level 3	0		(126)
Ending Balance	$ 2,040	2,040	71,204
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		0	319,249
Total Realized and Unrealized Gains (Losses) Included in Income			103,864
Purchases			0
Sales			(46,840)
Issuances			0
Distributions and Other Settlements			3,863
Transfers Out of Level 3			(380,136)
Ending Balance			0
Accounting Standards Update 2015-02 | 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
Ending Balance			3,291
Accounting Standards Update 2015-02 | Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 117,989
Ending Balance			$ 117,989