Acquisitions - Additional Information (Detail)			3 Months Ended		9 Months Ended
	Jul. 01, 2016 USD ($) Branch $ / shares shares	Jan. 07, 2016 USD ($) Branch $ / shares shares	Jun. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition, Contingent Consideration [Line Items]
Merger and acquisition integration-related expenses				$ 1,697,000		$ 4,103,000
Acquisition Related Costs [Member]
Business Acquisition, Contingent Consideration [Line Items]
Increase in goodwill			$ 685,000
Core Deposits [Member]
Business Acquisition, Contingent Consideration [Line Items]
Core deposit intangible					$ 2,500,000		$ 3,300,000
Harmony Bank [Member]
Business Acquisition, Contingent Consideration [Line Items]
Shares to receive by the acquiree at the time of merger | shares	1.25
Consideration paid through common stock | shares	3,201,109
Date of Agreement					Jul. 01, 2016
Consideration price per share | $ / shares	$ 14.31
Closing stock price per share | $ / shares	11.45
Average strike price | $ / shares	$ 9.07
Cash paid in connection with cancellation of the old stock options	$ 869,000
Allowance for loan and lease losses					$ 0
Estimated useful life of core deposit intangible					10 years
Harmony Bank [Member] | Core Deposits [Member]
Business Acquisition, Contingent Consideration [Line Items]
Core deposit intangible					$ 691,000
Harmony Bank [Member] | New Jersey [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of bank branches operated | Branch	3
Pascack Bancorp, Inc. [Member]
Business Acquisition, Contingent Consideration [Line Items]
Shares to receive by the acquiree at the time of merger | shares		0.9576
Consideration paid through common stock | shares		3,314,284
Date of Agreement					Jan. 07, 2016
Consideration price per share | $ / shares		$ 11.35
Average strike price | $ / shares		$ 7.37
Cash paid in connection with cancellation of the old stock options		$ 122,000
Allowance for loan and lease losses					$ 0
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
Pascack Bancorp, Inc. [Member] | Core Deposits [Member]
Business Acquisition, Contingent Consideration [Line Items]
Core deposit intangible					$ 1,500,000
Pascack Bancorp, Inc. [Member] | New Jersey [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of bank branches operated | Branch		8