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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Earnings Per Share, Basic [Abstract]
Net income	$ 13,479	$ 9,699	$ 36,801	$ 26,194
Less allocated income to unvested shares		27		74
Net income available to common shareholders-basic	13,479	9,672	36,801	26,120
Basic weighted average common shares	18,676,033	18,395,971	18,603,227	18,343,901
Basic earnings per common share	$ 0.72	$ 0.53	$ 1.98	$ 1.42
Net income available to common shareholders-diluted	$ 13,479	$ 9,673	$ 36,801	$ 26,122
Weighted average common shares	18,676,033	18,395,971	18,603,227	18,343,901
Stock options and performance shares	253,744	362,375	302,653	386,828
Diluted weighted average common shares	18,929,777	18,758,346	18,905,880	18,730,729
Diluted earnings per common share	$ 0.71	$ 0.52	$ 1.95	$ 1.39