Derivatives and Hedging Activities - Summary of Fair Values of Derivative Instruments on Balance Sheets (Detail) - USD ($) |
Sep. 30, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Derivatives, Fair Value [Line Items] | ||
| Other Asset Derivatives | $ 54,074,000 | $ 14,629,000 |
| Other Liability Derivatives | 57,486,000 | 16,205,000 |
| Interest Rate Swaps [Member] | Loan Swaps [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional or Contractual Amount | 610,062,000 | 399,860,000 |
| Other Asset Derivatives | 52,837,000 | 14,585,000 |
| Other Liability Derivatives | 57,201,000 | 16,117,000 |
| Interest Rate Loan Commitments [Member] | Other Contract [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional or Contractual Amount | 121,396,000 | 34,236,000 |
| Other Asset Derivatives | 1,237,000 | 44,000 |
| Forward TBA Contracts [Member] | Other Contract [Member] | ||
| Derivatives, Fair Value [Line Items] | ||
| Notional or Contractual Amount | 188,000,000.0 | 50,000,000.0 |
| Other Liability Derivatives | $ 285,000 | $ 88,000 |