Reconciliation of shares used to determine net income per share (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Disclosure [Line Items]
Net income	$ 4,469	$ 2,509
Weighted average number of shares - basic	24,334,966	23,785,556
Weighted average number of shares outstanding - diluted	26,751,714	25,848,956
Warrants
Earnings Per Share Disclosure [Line Items]
Shares underlying	476,877	139,938
Options
Earnings Per Share Disclosure [Line Items]
Shares underlying	1,939,871	1,923,462