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Share-Based Compensation - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2011
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Vesting description	one-third vesting in each year
Common Stock and Deferred Common Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting description	immediately
Restricted Stock and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Vesting description	one-third vesting in each year

Description of award terms as to how many shares or portion of an award are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, thereby giving the employee the legal right to convert the award to shares, to sell the shares, and be entitled to the cash proceeds of such sale. For example, vesting may be expressed as being 25 percent of the shares under option on each anniversary of the grant date.

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