Allowance for Credit Losses and Credit Quality - Rollfowards of the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for loan and lease losses
Balance, beginning of period	$ 113,052	$ 157,446	$ 171,041
Charge-offs	(86,515)	(97,935)	(84,728)
Recoveries	41,432	30,384	29,703
Net (charge-offs) recoveries	(45,083)	(67,551)	(55,025)
Provision for credit losses	252,073	65,282	46,768
Other	(166)	(42,125)	(5,338)
Balance, end of period	525,868	113,052	157,446
Unfunded commitments [Roll Forward]
Balance, beginning of period	3,528	1,428	1,479
Charge-offs	0	0	0
Recoveries	0	0	0
Net (charge-offs) recoveries	0	0	0
Provision for credit losses	5,078	233	(51)
Other	0	0	0
Balance, end of period	23,313	3,528	1,428
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period	116,580	158,874	172,520
Charge-offs	(86,515)	(97,935)	(84,728)
Recoveries	41,432	30,384	29,703
Net (charge-offs) recoveries	(45,083)	(67,551)	(55,025)
Provision for credit losses	257,151	65,515	46,717
Other	(166)	(42,125)	(5,338)
Balance, end of period	549,181	116,580	158,874
PCD Loans
Allowance for loan and lease losses
Addition due to merger		0
Unfunded commitments [Roll Forward]
Addition due to merger		1,867
Allowance for loan, leases and unfunded commitments [Roll Forward]
Addition due to merger		1,867
Consumer Loan Portfolio
Allowance for loan and lease losses
Balance, beginning of period	28,572	80,017	98,085
Charge-offs	(23,270)	(50,480)	(64,520)
Recoveries	15,527	23,653	26,487
Net (charge-offs) recoveries	(7,743)	(26,827)	(38,033)
Provision for credit losses	8,773	17,492	24,851
Other	(45)	(42,110)	(4,886)
Balance, end of period	136,894	28,572	80,017
Consumer Loan Portfolio | PCD Loans
Allowance for loan and lease losses
Addition due to merger		0
Commercial Loan and Lease Portfolio
Allowance for loan and lease losses
Balance, beginning of period	84,480	77,429	72,956
Charge-offs	(63,245)	(47,455)	(20,208)
Recoveries	25,905	6,731	3,216
Net (charge-offs) recoveries	(37,340)	(40,724)	(16,992)
Provision for credit losses	243,300	47,790	21,917
Other	(121)	(15)	(452)
Balance, end of period	388,974	84,480	$ 77,429
Commercial Loan and Lease Portfolio | PCD Loans
Allowance for loan and lease losses
Addition due to merger		0
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan and lease losses
Balance, beginning of period	205,992
Balance, end of period		205,992
Unfunded commitments [Roll Forward]
Balance, beginning of period	14,707
Balance, end of period		14,707
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period	220,699
Balance, end of period		220,699
Cumulative Effect, Period of Adoption, Adjustment | Consumer Loan Portfolio
Allowance for loan and lease losses
Balance, beginning of period	107,337
Balance, end of period		107,337
Cumulative Effect, Period of Adoption, Adjustment | Commercial Loan and Lease Portfolio
Allowance for loan and lease losses
Balance, beginning of period	98,655
Balance, end of period		98,655
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan and lease losses
Balance, beginning of period	319,044
Balance, end of period		319,044
Unfunded commitments [Roll Forward]
Balance, beginning of period	18,235
Balance, end of period		18,235
Allowance for loan, leases and unfunded commitments [Roll Forward]
Balance, beginning of period	337,279
Balance, end of period		337,279
Cumulative Effect, Period of Adoption, Adjusted Balance | Consumer Loan Portfolio
Allowance for loan and lease losses
Balance, beginning of period	135,909
Balance, end of period		135,909
Cumulative Effect, Period of Adoption, Adjusted Balance | Commercial Loan and Lease Portfolio
Allowance for loan and lease losses
Balance, beginning of period	$ 183,135
Balance, end of period		$ 183,135