Benefit Plans - Additional Information (Detail) - USD ($)		12 Months Ended
	Jan. 29, 2014	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 01, 2019	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net actuarial loss expected to be recognized as a component of net periodic pension expense		$ 952,000
Discount rate used to compute the obligation		3.32%	4.30%
Vesting percentage		8.33%
Projected benefit obligation		$ 175,405,000	$ 157,364,000
Salary expense		19,100,000	18,800,000	$ 10,800,000
Expense for contributions to savings and investment plan		$ 8,600,000	8,500,000	7,100,000
Shares of common stock available for issuance (in shares)		4,300,000
Stock-based compensation expense		$ 14,726,000	$ 19,472,000	$ 12,204,000
Unrecognized stock-based compensation		$ 15,600,000
Average remaining vesting, years		2 years
Award vesting period		1 year
Shares in connection with acquisition (in shares)		3,130,171	1,803,165	0
Shares outstanding in connection with acquisition (in shares)		3,453,516	1,051,787	446,980		732,489
Weighted average exercise price in connection with acquisition (in usd per share)		$ 8	$ 5	$ 0
Director Restricted Stock Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Additional fees	$ 0
Stock Options and Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Stock-based compensation expense		$ 15,000,000.0	$ 19,500,000	$ 12,200,000
Stock awards granted		$ 2,100,000	$ 4,300,000	$ 4,300,000
RSUs
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Vesting percentage		33.33%
Granted (in shares)		1,412,941	509,725	370,681
Vested (in shares)		500,204	503,879	0
Award vesting period		3 years
Time-based RSUs in connection with acquisition		0	336,379	0
Stock-based compensation		$ 3,600,000	$ 5,500,000	$ 3,800,000
RSUs | Employee Stock Incentive Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Weighted average grant date fair value (usd per share)		$ 10.43	$ 12.36	$ 11.05
Performance Shares
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Award vesting period		3 years
Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)		0	1,263,144	608,786
Vested (in shares)		547,653	1,128,521	736,575
Non-Employee Directors | Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)			60,000	45,000
Non-Management Director | Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Granted (in shares)			60,000	50,000
Qualified Plan | Fixed income securities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation percentage		50.00%
Cumulative annual real return		3.00%
Qualified Plan | Fixed income securities | Consumer Price Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period		5 years
Qualified Plan | Fixed income securities | Merrill Lynch Intermediate Government/Corporate Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period		3 years
Qualified Plan | Equity securities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Target asset allocation percentage		50.00%
Cumulative annual real return		7.00%
Qualified Plan | Equity securities | Consumer Price Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period		5 years
Qualified Plan | Equity securities | S&P 500 Index
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Cumulative annual real return, period		3 years
Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		$ 20,081,000	$ 18,708,000
Nonqualified Plan | Former Directors And Senior Management
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		451,000	512,000
Obligation included in other comprehensive loss, net of tax		803,000	872,000
Obligation included in other comprehensive loss, tax		314,000	345,000
Obligation included in other comprehensive loss, net of tax, amount expected to be reclassified		1,100,000
Oritani Financial Corp. | Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Split dollar life insurance liability		961,000
Other pension plan | Nonqualified Plan | Non Qualified Plans For Former Directors
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		1,600,000	$ 1,700,000
Other pension plan | Oritani Financial Corp. | Qualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Withdrawal liability					$ 3,000,000.0
Other pension plan | Oritani Financial Corp. | Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		$ 1,600,000
Benefits payment period		5 years
Benefit equalization plans | Oritani Financial Corp. | Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		$ 26,800,000
Executive Supplemental Retirement Income Agreement | Oritani Financial Corp. | Nonqualified Plan
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Projected benefit obligation		$ 13,000,000.0
Benefits payment period		20 years