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Summary of Awards Authorized (Detail) (Performance Shares)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Number of Shares Awarded	241,095	263,292	279,831	182,816
Potential Number of Performance-Based Shares to be Vested	241,096	263,292	534,477	36,562
Potential Number of Performance-Based Shares to be Vested period	2015	2014	2013	2013

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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