Investment Securities - Summary of Unrealized Losses on Available for Sale Securities (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 Investment		Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Number of investments in unrealized loss positions	39
Number of investment with unrealized losses	9
Investments that were in unrealized loss position	$ 101,224	[1]	$ 8,163
Unrealized Losses on Investments	$ 742	[1]	$ 270

[1] As of March 31, 2013, we identified a total of 39 investments that were in unrealized loss positions, of which 9 investments totaling $101.2 million with unrealized losses of $0.7 million have been in an impaired position for a period of time greater than 12 months. As of March 31, 2013, we do not intend to sell any impaired debt or equity securities prior to recovery of our adjusted cost basis, and it is more likely than not that we will not be required to sell any of our securities prior to recovery of our adjusted cost basis. Based on our analysis as of March 31, 2013, we deem all impairments to be temporary, and therefore 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 available-for-sale securities portfolio are reviewed and monitored on a quarterly basis.