Shareholders' Equity - Additional Information (Detail) (USD $)	9 Months Ended				9 Months Ended				9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Aug. 21, 2007	Sep. 30, 2014 Common Stock [Member]	Sep. 30, 2013 Common Stock [Member]	Dec. 31, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Sep. 30, 2014 Tri Counties Bank [Member]	Sep. 30, 2013 Tri Counties Bank [Member]	Sep. 30, 2014 Mellon Investor Services LLC [Member] Amendment [Member]
Class of Stock [Line Items]
Cash dividends received									$ 6,395,000	$ 6,080,000
Dividend payable by bank			44,548,000
Shareholder Rights Plan	Jun. 25, 2001
Percentage of restriction on acquiring outstanding common stock by person or group	15.00%
Amendment date of Right Plan											Jun. 04, 2014
Schedule expiration date plan											Jul. 01, 2014
Repurchase of common stock				500,000
Stock repurchase plan percentage of common stock				3.20%
Common stock, shares outstanding	16,139,414		16,076,662	15,814,662	16,139,414	16,076,662	16,076,662	16,000,838
Repurchased shares outstanding	166,600
Company's common stock in lieu of cash to exercise options to purchase shares	166,020				166,020	248,765
Market value of common stock	$ 2,875,000	$ 3,240,000			$ 2,875,000	$ 3,240,000