General (Details 5) (USD $) In Thousands, unless otherwise specified	0 Months Ended	6 Months Ended
Dec. 31, 2012	Jun. 30, 2013	Jun. 30, 2012
Short-term and long-term investments
Other-than-temporary unrealized losses	$ 0	$ 0
Realized gains or losses		0	0
Amortized Cost	233,749	255,169
Gross Unrealized Gains	70	24
Gross Unrealized Losses	(129)	(329)
Total, Estimated Fair Value	233,690	254,864
U.S. Government and agency securities
Short-term and long-term investments
Amortized Cost	1,065	1,068
Total, Estimated Fair Value	1,065	1,068
Obligations of government-sponsored enterprises
Short-term and long-term investments
Amortized Cost	6,126	8,430
Gross Unrealized Gains	4	1
Gross Unrealized Losses	(2)	(21)
Total, Estimated Fair Value	6,128	8,410
Corporate debt securities
Short-term and long-term investments
Amortized Cost	214,603	244,919
Gross Unrealized Gains	66	23
Gross Unrealized Losses	(122)	(307)
Total, Estimated Fair Value	214,547	244,635
Taxable municipal bonds
Short-term and long-term investments
Amortized Cost	11,805	602
Gross Unrealized Losses	(5)	(1)
Total, Estimated Fair Value	11,800	601
Certificates of deposit
Short-term and long-term investments
Amortized Cost	150	150
Total, Estimated Fair Value	$ 150	$ 150

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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This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

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- Definition

The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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