Shareholders' Equity - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	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	22,764,295		22,714,964		15,814,662
Repurchased shares outstanding	166,600
Maximum [Member]
Class of Stock [Line Items]
Dividend payable by bank			$ 52,798,000
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares outstanding	22,764,295	16,139,414	22,714,964	16,076,662
Company's common stock in lieu of cash to exercise options to purchase shares	30,321	103,268
Market value of common stock	$ 721,000	$ 2,551,000
Tri Counties Bank [Member]
Class of Stock [Line Items]
Cash dividends received	$ 8,968,000	$ 6,395,000