Income Per Common Share - Reconciliation of Weighted-Average Shares Used for the Basic Computation and that Used for the Diluted Computation (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted-average shares for basic	4,861,697	4,857,083	4,860,820	4,853,985
Dilutive effect of convertible preferred stock and stock options	71,085	74,152	73,427	75,074
Weighted-average shares for diluted	4,932,782	4,931,235	4,934,247	4,929,059