Acquisitions - Additional Information (Detail)			12 Months Ended
	Jul. 01, 2016 USD ($) Branch $ / shares shares	Jan. 07, 2016 USD ($) Branch $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Core deposit intangible			$ 2,400,000	$ 3,300,000
Goodwill			136,433,000	135,747,000
Merger and acquisition integration-related expenses			0	4,103,000	$ 1,152,000
Acquisition Related Costs
Business Acquisition, Contingent Consideration [Line Items]
Increase in goodwill			$ 685,000
Harmony Bank
Business Acquisition, Contingent Consideration [Line Items]
Shares to receive by the acquiree at the time of merger (in shares) | shares	1.25
Consideration paid through common stock | shares	3,201,109
Consideration price per share (usd per share) | $ / shares	$ 14.31
Closing stock price per share (usd per share) | $ / shares	11.45
Average strike price (usd per share) | $ / shares	$ 9.07
Cash paid in connection with cancellation of the old stock options	$ 869,000
Allowance for loan and lease losses	0
Core deposit intangible	691,000
Estimated useful life of core deposit intangible			10 years
Goodwill	$ 11,147,000			$ 11,100,000
Harmony Bank | New Jersey
Business Acquisition, Contingent Consideration [Line Items]
Number of bank branches operated | Branch	3
Pascack Bancorp, Inc.
Business Acquisition, Contingent Consideration [Line Items]
Shares to receive by the acquiree at the time of merger (in shares) | shares		0.9576
Consideration paid through common stock | shares		3,314,284
Consideration price per share (usd per share) | $ / shares		$ 11.35
Average strike price (usd per share) | $ / shares		$ 7.37
Cash paid in connection with cancellation of the old stock options		$ 122,000
Allowance for loan and lease losses		0
Core deposit intangible		$ 1,500,000
Estimated useful life of core deposit intangible		10 years
Percentage of aggregate merger consideration in shares		90.00%
Percentage of aggregate merger consideration in cash		10.00%
Cash paid for acquisition		$ 4,500,000
Goodwill		$ 15,311,000	$ 15,300,000
Pascack Bancorp, Inc. | New Jersey
Business Acquisition, Contingent Consideration [Line Items]
Number of bank branches operated | Branch		8