Investment Securities - Equity Investments (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Amortized Cost		$ 11,002,000	$ 23,856,000
Gross Unrealized Gain		185,000	46,190,000
Gross Unrealized Loss		1,646,000	0
Fair Value		9,541,000	70,046,000
Realized gain on sale of equity investment, net		22,052,000	0	$ 3,757,000
Unrealized gains on equity investments, net		761,000	26,175,000	20,745,000
Common Stock | Visa Class B shares
Investment Holdings [Line Items]
Amortized Cost		618,000	15,716,000
Gross Unrealized Gain		185,000	45,565,000
Gross Unrealized Loss		0	0
Fair Value		803,000	61,281,000
Realized gain on sale of equity investment, net		22,100,000	0	3,800,000
Unrealized gains on equity investments, net		3,000,000.0	25,600,000	20,700,000
Other equity investments
Investment Holdings [Line Items]
Amortized Cost		10,384,000	8,140,000
Gross Unrealized Gain		0	625,000
Gross Unrealized Loss		1,646,000	0
Fair Value		8,738,000	8,765,000
Impairment loss			$ 0
Spring EQ
Investment Holdings [Line Items]
Fair Value		4,200,000		$ 3,400,000
Impairment loss	$ 2,300,000
Consideration		$ 2,400,000