Shareholders' Equity - Additional Information (Detail) - USD ($) |
3 Months Ended | ||||
---|---|---|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Aug. 21, 2007 |
|
Class of Stock [Line Items] | |||||
Repurchase of common stock | 500,000 | ||||
Stock repurchase plan percentage of common stock | 3.20% | ||||
Common stock, shares outstanding | 22,956,323 | 22,955,963 | 15,814,662 | ||
Repurchased shares outstanding | 166,600 | ||||
Market value of common stock | $ 4,000 | $ 604,000 | |||
Maximum [Member] | |||||
Class of Stock [Line Items] | |||||
Cash dividend payable by bank | $ 85,254,000 | ||||
Tri Counties Bank [Member] | |||||
Class of Stock [Line Items] | |||||
Cash dividends received | $ 4,372,000 | $ 4,042,000 | |||
Common Stock [Member] | |||||
Class of Stock [Line Items] | |||||
Common stock, shares outstanding | 22,956,323 | 22,873,305 | 22,955,963 | 22,867,802 | |
Company's common stock in lieu of cash to exercise options to purchase shares | 134 | 16,251 | |||
Market value of common stock | $ 4,000 | $ 604,000 |