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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share Basic [Abstract]
Net income	$ 12,773	$ 7,644	$ 23,322	$ 16,495
Less allocated income to unvested shares	0	26	0	41
Net income	12,773	7,618	23,322	16,454
Basic weighted average common shares	18,600,186	18,353,174	18,566,235	18,317,452
Basic earnings per common share	$ 0.69	$ 0.42	$ 1.26	$ 0.90
Net income available to common shareholders-diluted	$ 12,773	$ 7,618	$ 23,322	$ 16,454
Weighted average common shares	18,600,186	18,353,174	18,566,235	18,317,452
Stock options and performance shares	294,699	359,125	319,149	396,324
Diluted weighted average common shares	18,894,885	18,712,299	18,885,384	18,713,776
Diluted earnings per common share	$ 0.68	$ 0.41	$ 1.23	$ 0.88