Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jul. 01, 2016	Jan. 07, 2016	May 31, 2013
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 136,433	$ 135,747
Core deposit intangible	2,400	3,300
Amortization of core deposit intangible	654	734	$ 415
Prior Acquisitions
Goodwill And Intangible Assets [Line Items]
Goodwill		110,000
Harmony Bank
Goodwill And Intangible Assets [Line Items]
Goodwill		$ 11,100		$ 11,147
Core deposit intangible				$ 691
Pascack Bancorp, Inc.
Goodwill And Intangible Assets [Line Items]
Goodwill	$ 15,300				$ 15,311
Core deposit intangible					$ 1,500
Somerset Hills Acquisition
Goodwill And Intangible Assets [Line Items]
Core deposit intangible						$ 2,700