Acquisitions - Summary of Estimated Fair Value of Acquired Assets and Liabilities Assumed at Date of Acquisition, Net of Cash Consideration Paid (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Jul. 01, 2016	Jan. 07, 2016
Business Acquisition [Line Items]
Goodwill	$ 136,433	$ 135,747
Harmony Bank
Business Acquisition [Line Items]
Cash and cash equivalents			$ 27,809
Securities available for sale			7,474
Securities held to maturity			6,885
Federal Home Loan Bank stock			780
Loans			259,985
Premises and equipment			3,125
Goodwill		$ 11,100	11,147
Identifiable intangible assets			1,088
Accrued interest receivable and other assets			8,146
Total assets acquired			326,439
Deposits			(278,060)
Other borrowings			(9,314)
Other liabilities			(2,411)
Total liabilities assumed			(289,785)
Net assets acquired			$ 36,654
Pascack Bancorp, Inc.
Business Acquisition [Line Items]
Cash and cash equivalents				$ 40,942
Securities held to maturity				3,925
Federal Home Loan Bank stock				2,962
Loans				319,575
Premises and equipment				14,438
Goodwill	$ 15,300			15,311
Identifiable intangible assets				1,514
Accrued interest receivable and other assets				6,672
Total assets acquired				405,339
Deposits				(304,466)
Other borrowings				(57,308)
Other liabilities				(6,344)
Total liabilities assumed				(368,118)
Net assets acquired				$ 37,221