Allowance for Credit Losses - Allowance for Credit Loss Activity (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 117,612	$ 62,224
Provision for credit losses on loans	3,301	18,430
Charge-offs	(6,532)	(11,430)
Recoveries	720	274
Net (Charge-offs)/Recoveries	(5,812)	(11,156)
Balance at End of Period	115,101	96,850	$ 62,224
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Commercial | Commercial real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	65,656	30,577
Provision for credit losses on loans	1,996	7,639
Charge-offs	(810)	(442)
Recoveries	0	27
Net (Charge-offs)/Recoveries	(810)	(415)
Balance at End of Period	66,842	42,611	$ 30,577
Commercial | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	16,100	15,681
Provision for credit losses on loans	2,728	6,196
Charge-offs	(4,302)	(9,879)
Recoveries	137	19
Net (Charge-offs)/Recoveries	(4,165)	(9,860)
Balance at End of Period	14,663	19,870	15,681
Commercial | Commercial construction
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,239	7,900
Provision for credit losses on loans	(911)	2,309
Charge-offs	0	(229)
Recoveries	1	2
Net (Charge-offs)/Recoveries	1	(227)
Balance at End of Period	6,329	6,606	7,900
Commercial | Business banking
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	15,917	0
Provision for credit losses on loans	514	1,194
Charge-offs	(917)	(460)
Recoveries	166	74
Net (Charge-offs)/Recoveries	(751)	(386)
Balance at End of Period	15,680	13,706	0
Consumer | Consumer real estate
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	10,014	6,337
Provision for credit losses on loans	(844)	472
Charge-offs	(271)	(172)
Recoveries	82	38
Net (Charge-offs)/Recoveries	(189)	(134)
Balance at End of Period	8,981	11,200	6,337
Consumer | Other consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,686	1,729
Provision for credit losses on loans	(182)	620
Charge-offs	(232)	(248)
Recoveries	334	114
Net (Charge-offs)/Recoveries	102	(134)
Balance at End of Period	$ 2,606	2,857	1,729
Impact of new accounting standard
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		27,352
Balance at End 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
Balance at End 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
Balance at End 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)
Balance at End 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
Balance at End 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
Balance at End 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
Balance at End of Period			$ 642