Allowance for Credit Losses - Allowance for Credit Loss Activity (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		$ 62,224	$ 60,996
Provision for credit losses on loans		131,421	14,873
Charge-offs		(106,365)	(16,189)
Recoveries		2,986	2,544
Net (Charge-offs)/Recoveries		(103,379)	(13,645)
Balance at End of Period		117,612	62,224
Customer fraud, check kiting
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Charge-offs	$ (58,700)
Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		30,577	33,707
Provision for credit losses on loans		56,489	397
Charge-offs		(26,460)	(3,664)
Recoveries		240	137
Net (Charge-offs)/Recoveries		(26,220)	(3,527)
Balance at End of Period		65,656	30,577
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		15,681	11,596
Provision for credit losses on loans		65,288	11,625
Charge-offs		(74,282)	(8,928)
Recoveries		1,560	1,388
Net (Charge-offs)/Recoveries		(72,722)	(7,540)
Balance at End of Period		16,100	15,681
Commercial | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		7,900	7,983
Provision for credit losses on loans		2,986	318
Charge-offs		(454)	(406)
Recoveries		183	5
Net (Charge-offs)/Recoveries		(271)	(401)
Balance at End of Period		7,239	7,900
Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		0
Provision for credit losses on loans		5,303
Charge-offs		(2,612)
Recoveries		328
Net (Charge-offs)/Recoveries		(2,284)
Balance at End of Period		15,917	0
Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		6,337	6,187
Provision for credit losses on loans		(368)	866
Charge-offs		(667)	(1,353)
Recoveries		187	637
Net (Charge-offs)/Recoveries		(480)	(716)
Balance at End of Period		10,014	6,337
Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		1,729	1,523
Provision for credit losses on loans		1,723	1,667
Charge-offs		(1,890)	(1,838)
Recoveries		488	377
Net (Charge-offs)/Recoveries		(1,402)	(1,461)
Balance at End of Period		2,686	1,729
Impact of ASU 2016-13 Adoption
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		27,346
Balance at End of Period			27,346
Impact of ASU 2016-13 Adoption | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		4,810
Balance at End of Period			4,810
Impact of ASU 2016-13 Adoption | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		7,853
Balance at End of Period			7,853
Impact of ASU 2016-13 Adoption | Commercial | Other Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		(3,376)
Balance at End of Period			(3,376)
Impact of ASU 2016-13 Adoption | Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		12,898
Balance at End of Period			12,898
Impact of ASU 2016-13 Adoption | Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		4,525
Balance at End of Period			4,525
Impact of ASU 2016-13 Adoption | Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		$ 636
Balance at End of Period			$ 636