Investment Securities - Available for sale sponsored funds with fair values below carrying values (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) security	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Unrealized losses
Securities in an unrealized loss position | security	1
Allowance for credit losses	$ 0
Net unrealized gains (losses) on trading debt securities	900	$ 400	$ (100)
Net unrealized gains (losses) on equity securities	12,300	25,000	$ (22,800)
Commercial paper
Fair value
Less than 12 months	2,414
Total fair value	2,414
Unrealized losses
Less than 12 months	(15)
Total unrealized losses	$ (15)
Corporate bonds
Fair value
Less than 12 months		4,538
12 months or longer		8,056
Total fair value		12,594
Unrealized losses
12 months or longer		(5)
Total unrealized losses		$ (5)