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Summary of Stock Option Activity (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares, Beginning Balance 7,029,360  
Options granted, Shares 1,729,922  
Options forfeited, Shares (269,792)  
Options expired, Shares (630,903)  
Options exercised, Shares (206,299)  
Number of shares, Ending Balance 7,652,288 7,029,360
Weighted average exercise price, Beginning Balance $ 7.67  
Options granted, Weighted average exercise price $ 4.97  
Options forfeited, Weighted average exercise price $ 5.64  
Options expired, Weighted average exercise price $ 5.82  
Options exercised, Weighted average exercise price $ 5.12  
Weighted average exercise price, Ending Balance $ 7.35 $ 7.67
Weighted average remaining contractual term, End of the period 6 years 8 months 19 days 6 years 3 months 11 days
Beginning Balance, Aggregate intrinsic value $ 506  
Ending Balance, Aggregate intrinsic value $ 11,392 $ 506