Amortized Cost and Fair Value of Marketable Securities Classified by Stated Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 117,861	$ 215,260
Fair value	118,187	214,944
Due in 1 year or less
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	53,761	70,871
Fair value	53,852	70,794
Due in 1 - 2 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	36,510	64,902
Fair value	36,694	64,754
Due in 2 - 3 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	11,847	37,493
Fair value	11,856	37,500
Due in 3 - 4 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	744	14,459
Fair value	746	14,387
Due in 4 - 9 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	5,158	12,759
Fair value	5,179	12,748
Due in 9 - 20 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,032	2,957
Fair value	1,040	2,958
Due in 20 - 32 years
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,809	11,819
Fair value	$ 8,820	$ 11,803

Amount of available-for-sale debt securities at cost, net of adjustments, which include, but are not limited to, accretion, amortization, collection of cash, previous other-than-temporary impairments (OTTI) recognized in earnings (less any cumulative-effect adjustments, as defined) and fair value hedge accounting adjustments.

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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.

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