Comprehensive Income - Components of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Equity [Abstract] | |||
| Net unrealized gains on available for sale securities | $ 2,145 | $ 4,040 | |
| Tax effect | (902) | (1,699) | |
| Unrealized holding gains on available for sale securities, net of tax | 1,243 | 2,341 | |
| Unfunded status of the supplemental retirement plans | (5,735) | (7,885) | |
| Tax effect | 2,411 | 3,315 | |
| Unfunded status of the supplemental retirement plans, net of tax | (3,324) | (4,570) | $ (1,269) |
| Joint beneficiary agreement liability | 303 | 26 | |
| Tax effect | 0 | 0 | |
| Joint beneficiary agreement liability, net of tax | 303 | 26 | |
| Accumulated other comprehensive loss | $ (1,778) | $ (2,203) | |