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Investments - Additional Information (Detail) (USD $)	12 Months Ended
Investments - Additional Information (Detail) (USD $)	Dec. 31, 2012
Available-for-sale Securities [Abstract]
Available for sale, gross unrealized term held	12 months
Other-than-temporary impairments considered	$ 0

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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