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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 129,851	$ 123,427	$ 137,208	$ 117,989
Total Realized and Unrealized Gains (Losses) Included in Income	21,096	11,566	33,094	55,030
Sales	(10,686)	(6,215)	(34,280)	(48,406)
Issuances	5,251	3,556	9,842	8,856
Distributions and Other Settlements	0	(15)	25	(15)
Transfers Out of Level 3	(252)	(486)	(629)	(1,621)
Ending Balance	145,260	131,833	145,260	131,833
Equity warrant assets | Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	127,811	120,037	135,168	114,698
Total Realized and Unrealized Gains (Losses) Included in Income	21,092	11,551	33,115	54,884
Sales	(10,682)	(6,215)	(34,276)	(48,374)
Issuances	5,251	3,556	9,842	8,856
Distributions and Other Settlements	0	0	0	0
Transfers Out of Level 3	(252)	(486)	(629)	(1,621)
Ending Balance	143,220	128,443	143,220	128,443
Non-marketable securities | Fair value accounting | Other venture capital investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	2,040	3,390	2,040	3,291
Total Realized and Unrealized Gains (Losses) Included in Income	4	15	(21)	146
Sales	(4)	0	(4)	(32)
Issuances	0	0	0	0
Distributions and Other Settlements	0	(15)	25	(15)
Transfers Out of Level 3	0	0	0	0
Ending Balance	$ 2,040	$ 3,390	$ 2,040	$ 3,390