Allowance for Credit Losses - Allowance for Credit Loss Activity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 115,101	$ 117,612	$ 96,850	$ 62,224	$ 117,612	$ 62,224
Provision for credit losses on loans	2,008		85,831		5,308	104,262
Charge-offs	(8,737)		(68,303)		(15,270)	(79,749)
Recoveries	1,264		231		1,985	520
Net (Charge-offs)/Recoveries	(7,473)		(68,072)		(13,285)	(79,229)
Balance at End of Period	109,636	$ 115,101	114,609	$ 96,850	109,636	114,609	$ 62,224
Accounting Standards Update [Extensible List]		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	66,842	$ 65,656	42,611	$ 30,577	65,656	30,577
Provision for credit losses on loans	2,937		20,681		4,933	28,345
Charge-offs	(7,558)		(5,600)		(8,369)	(6,042)
Recoveries	965		38		965	40
Net (Charge-offs)/Recoveries	(6,594)		(5,562)		(7,403)	(6,002)
Balance at End of Period	63,186	66,842	57,730	42,611	63,186	57,730	$ 30,577
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	14,663	16,100	19,870	15,681	16,100	15,681
Provision for credit losses on loans	225		60,906		2,953	67,104
Charge-offs	(473)		(61,616)		(4,774)	(71,496)
Recoveries	11		4		148	22
Net (Charge-offs)/Recoveries	(462)		(61,612)		(4,627)	(71,474)
Balance at End of Period	14,426	14,663	19,164	19,870	14,426	19,164	15,681
Commercial | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6,329	7,239	6,606	7,900	7,239	7,900
Provision for credit losses on loans	(426)		2,249		(1,337)	4,329
Charge-offs	0		0		0	0
Recoveries	2		19		3	21
Net (Charge-offs)/Recoveries	2		19		3	21
Balance at End of Period	5,905	6,329	8,874	6,606	5,905	8,874	7,900
Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	15,680	15,917	13,706	0	15,917	0
Provision for credit losses on loans	(560)		918		(46)	2,126
Charge-offs	(410)		(260)		(1,327)	(721)
Recoveries	47		40		213	101
Net (Charge-offs)/Recoveries	(363)		(220)		(1,115)	(620)
Balance at End of Period	14,756	15,680	14,404	13,706	14,756	14,404	0
Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	8,981	10,014	11,200	6,337	10,014	6,337
Provision for credit losses on loans	(410)		400		(1,254)	829
Charge-offs	(76)		(37)		(347)	(218)
Recoveries	152		22		234	112
Net (Charge-offs)/Recoveries	76		(15)		(113)	(106)
Balance at End of Period	8,647	8,981	11,585	11,200	8,647	11,585	6,337
Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,606	2,686	2,857	1,729	2,686	1,729
Provision for credit losses on loans	243		677		61	1,529
Charge-offs	(221)		(790)		(453)	(1,272)
Recoveries	88		108		423	224
Net (Charge-offs)/Recoveries	(132)		(682)		(30)	(1,048)
Balance at End of Period	$ 2,717	$ 2,606	2,852	2,857	$ 2,717	2,852	1,729
Impact of new accounting standard
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	27,352		27,352
Balance at End of Period				0			27,352
Impact of new accounting standard | Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	4,810		4,810
Balance at End of Period				0			4,810
Impact of new accounting standard | Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	7,853		7,853
Balance at End of Period				0			7,853
Impact of new accounting standard | Commercial | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	(3,376)		(3,376)
Balance at End of Period				0			(3,376)
Impact of new accounting standard | Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	12,898		12,898
Balance at End of Period				0			12,898
Impact of new accounting standard | Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			0	4,525		4,525
Balance at End of Period				0			4,525
Impact of new accounting standard | Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period			$ 0	642		$ 642
Balance at End of Period				$ 0			$ 642