Calculation of Net Income Per Basic and Diluted Share Attributable to Common Shareholders (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components Of Basic And Diluted Earning Per Share [Line Items]
Net income	$ 24,025	$ 17,972	$ 10,951
Less: dividends on redeemable convertible preferred stock		(4,179)	(4,179)
Less: undistributed earnings allocated to preferred shareholders		(4,507)	(2,377)
Net income attributable to common shareholders	$ 24,025	$ 9,286	$ 4,395
Basic-weighted-average shares outstanding:	23,373,593	12,352,004	11,079,432
Effect of dilutive securities:
Employee stock options, warrants and other	1,070,072	1,587,068	1,972,026
Diluted-weighted-average shares outstanding:	24,443,665	13,939,072	13,051,458
Net income per share attributable to common shareholders:
Basic	$ 1.03	$ 0.75	$ 0.40
Diluted	$ 0.98	$ 0.67	$ 0.34