Securities (Narrative) (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) security shares	Jun. 30, 2020 USD ($) shares	Sep. 30, 2021 USD ($) security shares	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale [Line Items]
Securities transfer from AFS to HTM, fair value			$ 2,012,123	$ 0
Debt Securities, Held-to-maturity, Allowance for Credit Loss	$ 0		0			$ 0
Debt Securities, Available-for-sale, Allowance for Credit Loss	0		0
Interest receivable	$ 52,886		$ 52,886			54,831
Visa Class B shares, shares sold | shares		17,360
Visa Class B shares, remaining shares | shares	77,683		77,683
Equity Securities	$ 13,425	$ 13,425	$ 13,425	$ 13,425	$ 13,425	13,425	$ 0
Available-for-sale Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Interest receivable	15,600		15,600			17,100
Held-to-maturity Securities
Debt Securities, Available-for-sale [Line Items]
Interest receivable	4,200		$ 4,200			$ 0
U.S. Government Agency and Government-Sponsored Enterprise Mortgage-Backed Securities and Collateralized Mortgage Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Securities transfer from AFS to HTM, fair value	2,010,000
Unrealized gain on AFS securities transferred to HTM, net of tax	$ 15,500
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	137		137
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	21		21
State and Municipal Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	109		109
U.S. Government and Government-Sponsored Enterprise Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | security	11		11