Marketable Securities Composition (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Maturities of less than five years	$ 52,012	$ 68,711
Maturities of more than ten years	4,661	6,946
Total marketable securities	56,673	75,657
Corporate and government bonds and notes and commercial paper
Schedule of Available-for-sale Securities [Line Items]
Short-term marketable securities	52,012	68,711
Federally-insured or FFELP guaranteed student loan auction rate securities
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 4,661	$ 6,946

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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+ Details

- Definition

Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature within one year from the balance sheet date or the normal operating cycle, whichever is longer.

+ References

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Total of debt securities categorized neither as held-to-maturity nor trading which are intended be sold or mature more than one year from the balance sheet date or operating cycle, if longer.

+ References

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