Loans Receivable, Net - Aging Analysis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	$ 11,293,891	$ 11,122,696
Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	9,541	17,123
Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	16,461	5,598
Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	5,172	1,725
Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	77,075	56,410
Non-accrual loans with no ACL	24,989	29,532
Non-accrual loans with ACL	20,912	2,432
Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	11,216,816	11,066,286
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	781,538	802,508
Residential real estate | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	0	6,058
Residential real estate | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	1,137	584
Residential real estate | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	52	934
Residential real estate | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	3,654	10,979
Non-accrual loans with no ACL	2,173	3,129
Non-accrual loans with ACL	292	274
Residential real estate | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	777,884	791,529
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	6,912,569	6,315,895
Commercial real estate | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,662	3,854
Commercial real estate | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	13,538	2,299
Commercial real estate | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,785	231
Commercial real estate | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	29,603	22,201
Non-accrual loans with no ACL	10,144	14,030
Non-accrual loans with ACL	474	1,787
Commercial real estate | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	6,882,966	6,293,694
Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,598,616	3,054,817
Other commercial | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,071	4,039
Other commercial | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	862	809
Other commercial | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,083	293
Other commercial | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	34,810	14,650
Non-accrual loans with no ACL	9,753	9,231
Non-accrual loans with ACL	20,041	278
Other commercial | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,563,806	3,040,167
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	660,920	636,405
Home equity | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,438	2,130
Home equity | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	656	756
Home equity | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	98	135
Home equity | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	5,649	5,734
Non-accrual loans with no ACL	2,406	2,664
Non-accrual loans with ACL	51	49
Home equity | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	655,271	630,671
Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	340,248	313,071
Other consumer | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,370	1,042
Other consumer | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	268	1,150
Other consumer | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	154	132
Other consumer | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	3,359	2,846
Non-accrual loans with no ACL	513	478
Non-accrual loans with ACL	54	44
Other consumer | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	$ 336,889	$ 310,225