General (Details 5) (USD $)	0 Months Ended	3 Months Ended
Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Short-term and long-term investments
Other-than-temporary unrealized losses	$ 0	$ 0
Realized gains or losses		0	0
Amortized Cost	233,749,000	250,190,000
Gross Unrealized Gains	70,000	53,000
Gross Unrealized Losses	(129,000)	(241,000)
Total, Estimated Fair Value	233,690,000	250,002,000
U.S. Government and agency securities
Short-term and long-term investments
Amortized Cost	1,065,000	1,065,000
Total, Estimated Fair Value	1,065,000	1,065,000
Obligations of government-sponsored enterprises
Short-term and long-term investments
Amortized Cost	6,126,000	8,449,000
Gross Unrealized Gains	4,000	4,000
Gross Unrealized Losses	(2,000)	(4,000)
Total, Estimated Fair Value	6,128,000	8,449,000
Corporate debt securities
Short-term and long-term investments
Amortized Cost	214,603,000	236,655,000
Gross Unrealized Gains	66,000	49,000
Gross Unrealized Losses	(122,000)	(232,000)
Total, Estimated Fair Value	214,547,000	236,472,000
Certificates of deposit
Short-term and long-term investments
Amortized Cost	150,000	150,000
Total, Estimated Fair Value	150,000	150,000
Taxable municipal bonds
Short-term and long-term investments
Amortized Cost	11,805,000	3,871,000
Gross Unrealized Losses	(5,000)	(5,000)
Total, Estimated Fair Value	$ 11,800,000	$ 3,866,000

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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