Loans Receivable, Net - Aging Analysis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	$ 11,238,048	$ 11,122,696
Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	8,677	17,123
Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	3,399	5,598
Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	4,220	1,725
Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	64,346	56,410
Non-accrual loans with no ACL	46,843	29,532
Non-accrual loans with ACL	1,207	2,432
Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	11,173,702	11,066,286
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	734,838	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	233	584
Residential real estate | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	338	934
Residential real estate | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	3,754	10,979
Non-accrual loans with no ACL	2,888	3,129
Non-accrual loans with ACL	295	274
Residential real estate | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	731,084	791,529
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	6,584,322	6,315,895
Commercial real estate | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	3,230	3,854
Commercial real estate | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	518	2,299
Commercial real estate | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,349	231
Commercial real estate | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	17,207	22,201
Non-accrual loans with no ACL	10,648	14,030
Non-accrual loans with ACL	462	1,787
Commercial real estate | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	6,567,115	6,293,694
Other commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,932,419	3,054,817
Other commercial | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	1,940	4,039
Other commercial | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,299	809
Other commercial | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	1,234	293
Other commercial | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	35,980	14,650
Non-accrual loans with no ACL	30,164	9,231
Non-accrual loans with ACL	343	278
Other commercial | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,896,439	3,040,167
Home equity
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	648,800	636,405
Home equity | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	1,808	2,130
Home equity | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	163	756
Home equity | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	155	135
Home equity | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	4,793	5,734
Non-accrual loans with no ACL	2,617	2,664
Non-accrual loans with ACL	50	49
Home equity | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	644,007	630,671
Other consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	337,669	313,071
Other consumer | Accruing loans 30-59 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	1,699	1,042
Other consumer | Accruing loans 60-89 days past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	186	1,150
Other consumer | Accruing loans 90 days or more past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	144	132
Other consumer | Past due
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	2,612	2,846
Non-accrual loans with no ACL	526	478
Non-accrual loans with ACL	57	44
Other consumer | Current loans receivable
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans receivable	$ 335,057	$ 310,225