Share-Based Compensation (Detail) (USD $)
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1 Months Ended | 3 Months Ended | 9 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 1 Months Ended | 3 Months Ended | 9 Months Ended | 1 Months Ended | |||||||||||||||||
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Dec. 10, 2010
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
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Sep. 30, 2011
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Jun. 01, 2010
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Sep. 30, 2012
Common Stock [Member]
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Sep. 30, 2011
Common Stock [Member]
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Sep. 30, 2012
Restricted Stock Units [Member]
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Sep. 30, 2011
Restricted Stock Units [Member]
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Sep. 30, 2011
Founders Grant Award [Member]
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Sep. 30, 2011
Founders Grant Award [Member]
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Nov. 14, 2007
Founders Grant Award [Member]
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Dec. 16, 2008
2008 Bonus Award [Member]
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Dec. 16, 2009
2009 Bonus Award [Member]
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Jun. 01, 2010
Performance Award [Member]
M
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Sep. 30, 2012
Performance Award [Member]
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Sep. 30, 2011
Performance Award [Member]
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Sep. 30, 2012
Performance Award [Member]
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Sep. 30, 2011
Performance Award [Member]
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Dec. 14, 2010
2010 Bonus Award [Member]
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Feb. 02, 2012
2011 Bonus Award [Member]
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Jun. 01, 2010
Unvested Restricted Stock Awards [Member]
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Jun. 01, 2010
Unvested Stock Options [Member]
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Nov. 14, 2009
Second Anniversary [Member]
Founders Grant Award [Member]
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Nov. 14, 2011
Third Anniversary [Member]
Founders Grant Award [Member]
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Nov. 14, 2010
Third Anniversary [Member]
Founders Grant Award [Member]
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||||||||||||||||||||||||||
Vesting period of awards | Four | Three | Three | Three | |||||||||||||||||||||||
Award vesting rights, percentage vested | 25.00% | 50.00% | 25.00% | 25.00% | |||||||||||||||||||||||
Aggregate fair value | $ 9,500,000 | $ 13,200,000 | $ 15,900,000 | $ 18,900,000 | $ 21,200,000 | ||||||||||||||||||||||
Fraction of bonus award vested per year | One-third | ||||||||||||||||||||||||||
Amount of the award granted to retirement - eligible employees | 4,200,000 | 5,100,000 | 6,200,000 | 6,700,000 | |||||||||||||||||||||||
Date of tranche of awards vested | January 9, 2012 | December 17, 2012 | |||||||||||||||||||||||||
Number of common shares reserved | 4,200,000 | 100,000 | |||||||||||||||||||||||||
Expected amount from the reserved stock | 1,300,000 | 16,700,000 | |||||||||||||||||||||||||
Length of performance award time-vest | 31 | ||||||||||||||||||||||||||
Award annual fraction of time-vesting | One-half | ||||||||||||||||||||||||||
CEO Award vesting period | 5 years | ||||||||||||||||||||||||||
Stock option award value | 3,600,000 | ||||||||||||||||||||||||||
Shares awarded to non-employee directors | 4,544 | 7,840 | 18,603 | 21,259 | |||||||||||||||||||||||
Share-based compensation expense | $ 7,500,000 | $ 7,900,000 | $ 19,409,000 | $ 24,322,000 | $ 900,000 | $ 2,500,000 | $ 600,000 | $ 400,000 | $ 1,400,000 | $ 4,200,000 |