The amount by which the fair value of an investment 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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+ Details

Investments - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
Investments - Additional Information (Detail) (USD $)	Dec. 31, 2012	Dec. 31, 2012 Securities	Dec. 31, 2012 Investment [Member]	Dec. 31, 2012 Marketable equity securities [Member]	Dec. 31, 2011 Marketable equity securities [Member]	Dec. 31, 2010 Marketable equity securities [Member]
Schedule of Investments [Line Items]
Investment concentration risk percentage			5.00%
Identification of potential other-than-temporary impairments		25.00%
Impairment of investments	$ 17,000			$ 700,000	$ 68,000	$ 43,000
Number of marketable equity securities in an unrealized loss position		152