Marketable Securities - Maturities of Held to Maturity Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Marketable Securities [Abstract]
Due within one year	$ 70,408
Due in one to five years	79,250
Total	$ 149,658

This item represents debt securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after one year and through five years from the balance sheet date and which are categorized as held-to-maturity.

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This item represents debt securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature within one year of the balance sheet date and which are categorized as held-to-maturity.

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