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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 131,022	$ 125,651	$ 137,208	$ 117,989
Total Realized and Unrealized Gains (Losses) Included in Income	4,848	23,249	11,997	43,464
Purchases	0	0	0	0
Sales	(8,178)	(27,393)	(23,594)	(42,190)
Issuances	2,218	2,811	4,592	5,298
Distributions and Other Settlements	(5)	0	25	0
Transfers Out of Level 3	(54)	(891)	(377)	(1,134)
Ending Balance	129,851	123,427	129,851	123,427
Equity warrant assets | Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	128,982	122,261	135,168	114,698
Total Realized and Unrealized Gains (Losses) Included in Income	4,843	23,249	12,022	43,333
Purchases	0	0	0	0
Sales	(8,178)	(27,393)	(23,594)	(42,158)
Issuances	2,218	2,811	4,592	5,298
Distributions and Other Settlements	0	0	0	0
Transfers Out of Level 3	(54)	(891)	(377)	(1,134)
Ending Balance	127,811	120,037	127,811	120,037
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	3,390	2,040	3,291
Total Realized and Unrealized Gains (Losses) Included in Income	5	0	(25)	131
Purchases	0	0	0	0
Sales	0	0	0	(32)
Issuances	0	0	0	0
Distributions and Other Settlements	(5)	0	25	0
Transfers Out of Level 3	0	0	0	0
Ending Balance	$ 2,040	$ 3,390	$ 2,040	$ 3,390