Earnings Per Share - Summary Of Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Basic [Abstract]
Net income, as reported	$ 9,699	$ 7,121	$ 26,194	$ 20,127
Less allocated income to unvested shares	27	6	74	12
Net income available to common shareholders-basic	9,672	7,115	26,120	20,115
Basic weighted average common shares	18,395,971	18,173,062	18,343,901	18,154,768
Basic earnings per common share	$ 0.53	$ 0.39	$ 1.42	$ 1.11
Net income available to common shareholders-diluted	$ 9,673	$ 7,116	$ 26,122	$ 20,116
Weighted average common shares	18,395,971	18,173,062	18,343,901	18,154,768
Stock options and performance shares	362,375	407,021	386,828	428,311
Diluted weighted average common shares	18,758,346	18,580,083	18,730,729	18,583,079
Diluted earnings per common share	$ 0.52	$ 0.38	$ 1.39	$ 1.08