Shareholders' Equity - Additional Information (Detail) (USD $)	6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Aug. 21, 2007	Jun. 30, 2014 Common Stock [Member]	Jun. 30, 2013 Common Stock [Member]	Dec. 31, 2013 Common Stock [Member]	Dec. 31, 2012 Common Stock [Member]	Jun. 30, 2014 Mellon Investor Services LLC [Member] Amendment [Member]	Jun. 30, 2014 Tri Counties Bank [Member]	Jun. 30, 2013 Tri Counties Bank [Member]
Class of Stock [Line Items]
Cash dividends received										$ 4,100,000	$ 3,780,000
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%
Portion of market value to acquire common stock or shares	One-half of market value
Initial exercise price of rights	49.00
Redemption price of rights	0.01
Schedule expiration date plan	Jul. 10, 2011								Jul. 01, 2014
Amendment date of Right Plan	Jul. 08, 2011								Jun. 04, 2014
Extended maturity date of Right Plan	Jul. 10, 2021
Repurchase of common stock				500,000
Stock repurchase plan percentage of common stock				3.20%
Common stock, shares outstanding	16,133,414		16,076,662	15,814,662	16,133,414	16,065,469	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	160,020				103,268	166,134
Market value of common stock	$ 2,786,000	$ 2,937,000			$ 2,786,000	$ 2,937,000