Fair Value of Financial Instruments - Additional Information about Level 3 Assets Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 148,211	$ 138,754	$ 146,278	$ 122,250
Total Realized and Unrealized Gains Included in Income	39,584	32,237	105,350	69,179
Purchases	0	0	575	0
Sales/Exits	(45,634)	(34,101)	(114,103)	(61,464)
Issuances	4,130	4,809	11,714	14,007
Distributions and Other Settlements	0	0	3	0
Transfers Out of Level 3	(1,116)	(209)	(4,642)	(2,482)
Ending Balance	145,175	141,490	145,175	141,490
Fair value accounting | Equity warrant assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	147,770	137,753	145,199	121,331
Total Realized and Unrealized Gains Included in Income	39,527	32,237	105,338	69,097
Purchases	0	0	575	0
Sales/Exits	(45,270)	(34,101)	(113,143)	(61,464)
Issuances	4,130	4,809	11,714	14,007
Distributions and Other Settlements	0	0	0	0
Transfers Out of Level 3	(1,116)	(209)	(4,642)	(2,482)
Ending Balance	145,041	140,489	145,041	140,489
Fair value accounting | Non-marketable securities | Unconsolidated venture capital and private equity fund investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	441	1,001	1,079	919
Total Realized and Unrealized Gains Included in Income	57	0	12	82
Purchases	0	0	0	0
Sales/Exits	(364)	0	(960)	0
Issuances	0	0	0	0
Distributions and Other Settlements	0	0	3	0
Transfers Out of Level 3	0	0	0	0
Ending Balance	$ 134	$ 1,001	$ 134	$ 1,001