Quarterly report pursuant to Section 13 or 15(d)

Summary of Share Activity Related to Restricted Stock Units (Detail)

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Summary of Share Activity Related to Restricted Stock Units (Detail) (Restricted Stock Units (RSUs), USD $)
3 Months Ended
Mar. 31, 2013
Restricted Stock Units (RSUs)
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Shares, Nonvested, beginning of period 969,820
Shares, Granted 1,171 [1]
Shares, Vested   
Shares, Forfeited (11,293)
Shares, Nonvested, end of period 959,698
Weighted Average Grant Date Value Per Share, Beginning of period $ 22.70
Weighted Average Grant Date Fair Value Per Share, Granted $ 18.39 [1]
Weighted Average Grant Date Fair Value Per Share, Vested   
Weighted Average Grant Date Fair Value Per Share, Forfeited $ 19.26
Weighted Average Grant Date Value Per Share, End of period $ 22.73
[1] Adjustments to amounts granted in 2012.