Earnings Per Share - Summary Of Earnings Per Share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share Basic [Abstract]
Net income, as reported	$ 7,644	$ 3,445	$ 16,495	$ 13,006
Less allocated income to unvested shares	26	2	41	5
Net income available to common shareholders-basic	7,618	3,443	16,454	13,001
Basic weighted average common shares	18,353,174	18,150,306	18,317,452	18,145,525
Basic earnings per common share	$ 0.42	$ 0.19	$ 0.90	$ 0.72
Net income available to common shareholders-diluted	$ 7,619	$ 3,443	$ 16,455	$ 13,002
Weighted average common shares	18,353,174	18,150,306	18,317,452	18,145,525
Stock options and performance shares	359,125	438,189	396,324	440,631
Diluted weighted average common shares	18,712,299	18,588,495	18,713,776	18,586,156
Diluted earnings per common share	$ 0.41	$ 0.19	$ 0.88	$ 0.70