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Summary of Stock Option (Detail) (USD $)
 3 Months Ended
Mar. 31, 2013
Options  
Beginning Balance 2,528,177
Grants 100,000
Exercises (64,397)
Cancellations (45,000)
Ending Balance 2,518,780
Options exercisable at End of Period 1,564,405
Weighted-average exercise price  
Beginning Balance $ 13.06
Grants $ 10.72
Exercises $ 4.69
Cancellations $ 19.37
Ending Balance $ 13.07
Options exercisable at End of Period $ 14.32
Weighted Average Remaining Contractual Term  
Options outstanding, Ending balance 5 years 11 months 1 day
Options exercisable, Ending balance 4 years 10 months 13 days
Aggregate Intrinsic Value  
Options outstanding, end of period $ 4,839,538
Options exercisable, end of period $ 3,907,931