Gross Realized Investment and Other Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Available For Sale Securities [Line Items]
Investment income	$ 13,809	$ 15,505	$ 18,397
Realized gains	9,417	12,151	24,055
Realized losses	(1,839)	(9,849)	(2,273)
Investment and other gains (losses)	7,578	2,302	21,782
Debt securities
Available For Sale Securities [Line Items]
Investment income	12,399	13,860	15,014
Short-term investments
Available For Sale Securities [Line Items]
Investment income	$ 1,410	$ 1,645	$ 3,383

- Definition

This item represents investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities, and income or expense derived from the amortization of investment related discounts or premiums, respectively, net of related investment expenses. This item does not include realized or unrealized gains or losses on the sale or holding of investments in debt and equity securities required to be included in earnings for the period or for other than temporary losses related to investments in debt and equity securities which are included in realized losses in the period recognized, and does not include investment income from real or personal property, such as rental income.

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