Shareholders' Equity - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	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	22,822,325		22,775,173		15,814,662
Repurchased shares outstanding	166,600
Market value of common stock	$ 2,331,000	$ 667,000
Maximum [Member]
Class of Stock [Line Items]
Cash dividend payable by bank			$ 73,297,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares outstanding	22,822,325	22,749,523	22,775,173	22,714,964
Company's common stock in lieu of cash to exercise options to purchase shares	96,996	29,441
Market value of common stock	$ 2,666,000	$ 699,000
Tri Counties Bank [Member]
Class of Stock [Line Items]
Cash dividends received	$ 7,338,000	$ 5,713,000