Investment Securities Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Amortized cost		$ 3,009,064
Available-for-sale Securities, Fair Value Disclosure		3,097,375		$ 3,062,143
HTM, at amortized cost		824,283		278,281
HTM securities		826,932
Proceeds from sales of AFS securities		125,811	$ 187,819
Debt extinguishment costs	$ 32,200
Debt extinguishment costs	841
Marketable Securities, Unrealized Gain (Loss)	(400)
Visa
Schedule of Investments [Line Items]
Gain on sale of shares	34,000	34,000
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Amortized cost		201,654		373,779
Available-for-sale Securities, Fair Value Disclosure		201,547		377,998
HTM, at amortized cost		439,220		278,281
HTM securities		449,671		296,857
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Amortized cost		1,002,146		891,327
Available-for-sale Securities, Fair Value Disclosure		1,055,462		952,613
Auction Rate Securities [Member]
Schedule of Investments [Line Items]
Amortized cost		76,350		101,510
Available-for-sale Securities, Fair Value Disclosure		74,834		98,206
Proceeds from sales of AFS securities	$ 24,600
Collateral Pledged [Member]
Schedule of Investments [Line Items]
Securities pledged as collateral		$ 2,000,000		$ 520,500