Loans and Allowance for Credit Losses for Loans - Summary of Activity in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Allowance for loan losses:
Beginning balance	$ 339,324	$ 309,614	$ 340,243	$ 161,759
Loans charged-off	(2,019)	(17,125)	(23,193)	(40,087)
Charged-off loans recovered	1,726	1,710	7,479	5,120
Net (charge-offs) recoveries	(293)	(15,415)	(15,714)	(34,967)
Provision (credit) for loan losses	3,496	30,833	17,998	105,709
Ending balance	342,527	325,032	342,527	325,032
Allowance for PCD loans reclassification				61,600
Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				92,531
Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses:
Beginning balance				254,290
Commercial and industrial
Allowance for loan losses:
Beginning balance	109,689	132,039	131,070	104,059
Loans charged-off	(1,248)	(13,965)	(19,283)	(31,349)
Charged-off loans recovered	514	428	2,781	1,796
Net (charge-offs) recoveries	(734)	(13,537)	(16,502)	(29,553)
Provision (credit) for loan losses	(5,078)	11,907	(10,691)	40,734
Ending balance	103,877	130,409	103,877	130,409
Commercial and industrial | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				15,169
Commercial and industrial | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses:
Beginning balance				119,228
Commercial Real Estate
Allowance for loan losses:
Beginning balance	189,139	131,702	164,113	45,673
Loans charged-off	0	(695)	(382)	(766)
Charged-off loans recovered	29	100	763	244
Net (charge-offs) recoveries	29	(595)	381	(522)
Provision (credit) for loan losses	10,553	13,543	35,227	49,702
Ending balance	199,721	144,650	199,721	144,650
Commercial Real Estate | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				49,797
Commercial Real Estate | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses:
Beginning balance				95,470
Residential Mortgage
Allowance for loan losses:
Beginning balance	25,303	29,630	28,873	5,060
Loans charged-off	0	(7)	(139)	(348)
Charged-off loans recovered	228	31	576	626
Net (charge-offs) recoveries	228	24	437	278
Provision (credit) for loan losses	(799)	(1,040)	(4,578)	2,701
Ending balance	24,732	28,614	24,732	28,614
Residential Mortgage | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				20,575
Residential Mortgage | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses:
Beginning balance				25,635
Consumer
Allowance for loan losses:
Beginning balance	15,193	16,243	16,187	6,967
Loans charged-off	(771)	(2,458)	(3,389)	(7,624)
Charged-off loans recovered	955	1,151	3,359	2,454
Net (charge-offs) recoveries	184	(1,307)	(30)	(5,170)
Provision (credit) for loan losses	(1,180)	6,423	(1,960)	12,572
Ending balance	$ 14,197	$ 21,359	$ 14,197	21,359
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses:
Beginning balance				6,990
Consumer | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses:
Beginning balance				$ 13,957