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
	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 137,208	$ 117,989
Total Realized and Unrealized Gains (Losses) Included in Income	7,149	20,215
Purchases	0	0
Sales	(15,416)	(14,797)
Issuances	2,374	2,487
Distributions and Other Settlements	30	0
Transfers Out of Level 3	(323)	(243)
Ending Balance	131,022	125,651
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	7,179	20,084
Purchases	0	0
Sales	(15,416)	(14,765)
Issuances	2,374	2,487
Distributions and Other Settlements	0	0
Transfers Out of Level 3	(323)	(243)
Ending Balance	128,982	122,261
Non-marketable securities | Fair value accounting
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	2,040	3,291
Total Realized and Unrealized Gains (Losses) Included in Income	(30)	131
Purchases	0	0
Sales	0	(32)
Issuances	0	0
Distributions and Other Settlements	30	0
Transfers Out of Level 3	0	0
Ending Balance	2,040	3,390
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	3,291
Total Realized and Unrealized Gains (Losses) Included in Income	(30)	131
Purchases	0	0
Sales	0	(32)
Issuances	0	0
Distributions and Other Settlements	30	0
Transfers Out of Level 3	0	0
Ending Balance	$ 2,040	$ 3,390