Summary of Available-for-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Amortized cost	$ 99,477	$ 97,612
Unrealized gains (losses), net	1,122	922
Estimated fair value	100,599	98,534
Short term deposits
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Amortized cost	2,785	2,708
Unrealized gains (losses), net
Estimated fair value	2,785	2,708
U.S. GSE securities
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Amortized cost	2,957	1,506
Unrealized gains (losses), net	3	4
Estimated fair value	2,960	1,510
Corporate debt securities
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Amortized cost	93,735	93,398
Unrealized gains (losses), net	1,119	918
Estimated fair value	$ 94,854	$ 94,316

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

+ References+ Details