Derivatives - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Commercial Loans [Member] | Interest Rate Swap
Derivative [Line Items]
Derivative notional amount	$ 15,500,000	$ 2,500,000
Interest rate derivative assets, at fair value	372,000	56,000
Interest rate derivative liabilities, at fair value	421,000	62,000
Difference in fair value	43,000	6,000
Written And Purchased Certificate Of Deposit Option [Member]
Derivative [Line Items]
Options increased (decreased)	(22,000)	(548,000)
Interest rate derivative assets, at fair value	$ 239,000	$ 261,000