Derivatives and Hedging Activities - Summary of Fair Values of Derivative Instruments on Balance Sheets (Detail) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	$ 320,100,000	$ 229,800,000
Asset Derivatives	13,339,000	4,775,000
Liability Derivatives	14,940,000	5,315,000
Interest Rate Swaps [Member] | Loan Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	320,134,000	229,778,000
Asset Derivatives	13,281,000	4,650,000
Liability Derivatives	14,774,000	5,081,000
Interest Rate Loan Commitments [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	44,062,000	16,113,000
Asset Derivatives	58,000	125,000
Forward TBA Contracts [Member] | Other Contract [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	61,000,000	20,000,000
Liability Derivatives	$ 166,000	$ 234,000