Balance Sheet Offsetting - Summary of Valley's Financial Instruments that are Eligible for Offset (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Offsetting Liabilities
Gross Amounts Recognized	$ 393,733	$ 172,907
Gross Amounts Offset	0	0
Net Amounts Presented	393,733	172,907
Gross Amounts Not Offset, Financial Instruments	(118)	(1,214)
Gross Amounts Not Offset, Cash Collateral	(366,881)	(151,852)
Net Amount	26,734	19,841
Repurchase agreements
Offsetting Liabilities
Gross Amounts Recognized	350,000	150,000
Gross Amounts Offset	0	0
Total long-term securities sold under agreements to repurchase	350,000	150,000
Gross Amounts Not Offset, Financial Instruments	0	0
Gross Amounts Not Offset, Cash Collateral	(350,000)	(150,000)
Net Amount	0	0
Interest rate swaps
Offsetting Assets
Gross Amounts Recognized	158,382	48,642
Gross Amounts Offset	0	0
Net Amounts Presented	158,382	48,642
Gross Amounts Not Offset, Financial Instruments	(118)	(1,214)
Gross Amounts Not Offset, Cash Collateral	0	0
Net Amount	158,264	47,428
Offsetting Liabilities
Gross Amounts Recognized	43,733	22,907
Gross Amounts Offset	0	0
Net Amounts Presented	43,733	22,907
Gross Amounts Not Offset, Financial Instruments	(118)	(1,214)
Gross Amounts Not Offset, Cash Collateral	(16,881)	(1,852)
Net Amount	$ 26,734	$ 19,841