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Stock-based Compensation - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Performance Unit Awards 2009
      
Compensation Related Costs Share Based Payments Disclosure [Line Items]      
Performance period   The performance period for the 2009 Performance Units was the period from April 1, 2009 through March 31, 2012.  
Award description   Generally, the recipients would receive a target payment if the Company’s total shareholder return was positive and, when compared to the peer group, was at or above the 50th percentile but less than the 75th percentile and two times the target if at the 75th percentile or higher. The total target amount with respect to the 2009 Performance Units was approximately $3.4 million. If the Company’s total shareholder return was positive, and, when compared to the peer group, was at or above the 25th percentile but less than the 50th percentile, the recipients would only receive one-half of the target payment.  
Base payment   $ 1.7  
Pro-rated obligation   3.4  
Compensation expense (benefit) $ 1.0 $ (1.9) $ 2.2
Performance Unit Awards 2009 | Minimum
      
Compensation Related Costs Share Based Payments Disclosure [Line Items]      
Performance period   April 1, 2009  
Performance Unit Awards 2009 | Maximum
      
Compensation Related Costs Share Based Payments Disclosure [Line Items]      
Performance period   March 31, 2012  
Performance Unit Awards
      
Compensation Related Costs Share Based Payments Disclosure [Line Items]      
Performance period   The performance period for the Stock-Settled Performance Units is the three year period commending on April 1 of the year of grant, but can extend for an additional two years in certain circumstances.  
Performance Unit Awards 2010
      
Compensation Related Costs Share Based Payments Disclosure [Line Items]      
Award description   Generally, the recipients will receive a target number of shares if the Company's total shareholder return is positive and, when compared to the peer group, is at the 50thpercentile and two times the target if at the 75thpercentile or higher.If the Company's total shareholder return is positive, and, when compared to the peer group, is at or above the 25thpercentile, but less than the 50thpercentile, the recipients will only receive one-half of the target number of shares. The grant of shares when achievement is between the 25thand 75thpercentile will be determined on a pro-rata basis.