Allowance for Credit Losses - Allowance for Credit Loss Activity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 109,636	$ 114,609	$ 117,612	$ 62,224
Provision for credit losses on loans	2,302	19,302	7,612	123,564
Charge-offs	(4,207)	(13,667)	(19,477)	(93,416)
Recoveries	616	754	2,601	1,274
Net (Charge-offs)/Recoveries	(3,591)	(12,913)	(16,876)	(92,142)
Balance at End of Period	$ 108,348	$ 120,998	$ 108,348	$ 120,998
Accounting Standards Update [Extensible List]	ASU No. 2016-13	ASU No. 2016-13	ASU No. 2016-13	ASU No. 2016-13
Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 63,186	$ 57,730	$ 65,656	$ 30,577
Provision for credit losses on loans	(7,856)	23,839	(2,922)	52,185
Charge-offs	(3,661)	(10,187)	(12,030)	(16,229)
Recoveries	1	172	966	211
Net (Charge-offs)/Recoveries	(3,660)	(10,015)	(11,064)	(16,018)
Balance at End of Period	51,670	71,554	51,670	71,554
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	14,426	19,164	16,100	15,681
Provision for credit losses on loans	11,599	(4,155)	14,552	62,949
Charge-offs	(2)	(1,196)	(4,777)	(72,692)
Recoveries	216	398	364	420
Net (Charge-offs)/Recoveries	214	(798)	(4,413)	(72,272)
Balance at End of Period	26,239	14,211	26,239	14,211
Commercial | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	5,905	8,874	7,239	7,900
Provision for credit losses on loans	1,391	(1,617)	54	2,712
Charge-offs	(56)	0	(56)	0
Recoveries	2	1	5	22
Net (Charge-offs)/Recoveries	(54)	1	(51)	22
Balance at End of Period	7,242	7,258	7,242	7,258
Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	14,756	14,404	15,917	0
Provision for credit losses on loans	(2,689)	2,072	(2,736)	4,197
Charge-offs	(167)	(1,748)	(1,494)	(2,469)
Recoveries	241	64	454	166
Net (Charge-offs)/Recoveries	74	(1,684)	(1,040)	(2,303)
Balance at End of Period	12,141	14,792	12,141	14,792
Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	8,647	11,585	10,014	6,337
Provision for credit losses on loans	(80)	(797)	(1,335)	32
Charge-offs	(76)	(252)	(422)	(470)
Recoveries	33	41	267	153
Net (Charge-offs)/Recoveries	(43)	(211)	(155)	(317)
Balance at End of Period	8,524	10,577	8,524	10,577
Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,717	2,852	2,686	1,729
Provision for credit losses on loans	(63)	(40)	(1)	1,489
Charge-offs	(245)	(284)	(698)	(1,556)
Recoveries	123	78	545	302
Net (Charge-offs)/Recoveries	(122)	(206)	(153)	(1,254)
Balance at End of Period	$ 2,532	$ 2,606	$ 2,532	2,606
Impact of new accounting standard
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				27,352
Impact of new accounting standard | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				4,810
Impact of new accounting standard | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				7,853
Impact of new accounting standard | Commercial | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(3,376)
Impact of new accounting standard | Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				12,898
Impact of new accounting standard | Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				4,525
Impact of new accounting standard | Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ 642