Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 01, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 0	$ 0	$ 0
Impairment of core deposits and intangibles	0	0	0
Amortization expense - other intangible assets	$ 18,100,000	18,400,000	10,000,000.0
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
Residential mortgage
Finite-Lived Intangible Assets [Line Items]
Aggregate principal balances of mortgage loans serviced	$ 3,400,000,000	$ 3,200,000,000	$ 2,800,000,000
Oritani Financial Corp.
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible assets				$ 20,690,000
Oritani Financial Corp. | Core deposits
Finite-Lived Intangible Assets [Line Items]
Weighted average amortization period, years	10 years