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Shareholders' Equity - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Common Stock And Option Exercises [Line Items]
Common stock repurchased	276,995
Aggregate purchase price of common stock	$ 220,128
Stock option exercised	174,000

Number of share options (or share units) exercised during the current period.

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.