Derivatives and Hedging Activities - Summary of Fair Values of Derivative Instruments on Balance Sheets (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	$ 315,700,000	$ 229,800,000
Asset Derivatives	18,880,000	4,775,000
Liability Derivatives	20,729,000	5,315,000
Interest Rate Swaps [Member] | Loan Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	315,657,000	229,778,000
Asset Derivatives	18,672,000	4,650,000
Liability Derivatives	20,721,000	5,081,000
Interest Rate Loan Commitments [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	45,727,000	16,113,000
Asset Derivatives		125,000
Liability Derivatives	8,000
Forward TBA Contracts [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	73,000,000	20,000,000
Asset Derivatives	$ 208,000
Liability Derivatives		$ 234,000