Acquisition - Additional Information (Detail)		1 Months Ended		3 Months Ended							12 Months Ended
	Jul. 03, 2016 USD ($) Office	Dec. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Business acquisition, date											Jul. 01, 2016
Reversal of special bonus paid			$ 1,600,000
Income tax expense (benefit)				$ 10,000		$ 3,000	$ (103,000)	$ (1,000)	$ (1,000)	$ (3,000)	$ 13,000	$ (108,000)
Pro Forma [Member]
Business Acquisition [Line Items]
Income tax expense (benefit)											$ 0
First Eastern Bankshares Corporation [Member]
Business Acquisition [Line Items]
Cash payment to acquisition	$ 14,100,000
Number of residential loan production office | Office	8
Business acquisition additional cash payments		$ 175,000			$ 175,000