Summary of Unrealized Losses on Available for Sale Investment Securities (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2011 Investment Year		Dec. 31, 2010
Investments, Unrealized Loss Position [Line Items]
Number of investments in unrealized loss positions	85
12 months or longer - Fair Value of Investments	$ 44,606	[1]	$ 3,451
12 months or longer - Unrealized Losses	$ 33	[1]	$ 72

[1] As of September 30, 2011, we identified a total of 85 investments that were in unrealized loss positions, of which one investment totaling $44.6 million with unrealized losses of $33 thousand has been in an impaired position for a period of time greater than 12 months. Based on the underlying credit quality of the investments, we do not intend to sell any of our securities prior to recovery of our adjusted cost basis and as of September 30, 2011, it is more likely than not that we will not be required to sell any of our debt securities prior to recovery of our adjusted cost basis. Based on our analysis as of September 30, 2011, we deem all impairments to be temporary and changes in value for our temporarily impaired securities as of the same date are included in other comprehensive income. Market valuations and impairment analyses on assets in the investment securities portfolio are reviewed and monitored on a quarterly basis.