Goodwill and Other Intangible Assets - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0
Impairment of core deposits and intangibles	0	0	0
Net impairment (recovery of impairment) on loan servicing rights	(818,000)	36,000	388,000
Amortization expense - other intangible assets	24,600,000	18,100,000	18,400,000
Residential mortgage
Finite-Lived Intangible Assets [Line Items]
Aggregate principal balances of mortgage loans serviced	$ 3,500,000,000	$ 3,400,000,000	$ 3,200,000,000
Core deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	8 years 10 months 24 days
Other
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	7 years 7 months 6 days
Oritani Financial Corp.
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible assets	$ 20,700,000