Schedule of Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2012
Schedule Of Stock Options [Line Items]
Outstanding, Beginning Balance	1,737,881
Number of Shares, Granted	589,934
Number of Shares, Exercised	(584,859)
Number of Shares, Expired	(32,800)
Number of Shares, Cancelled	(9,697)
Outstanding, Ending Balance	1,700,459
Exercisable, Ending Balance	814,251