Marketable Securities, Available-for-sale (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Contractual maturity:
ESTIMATED FAIR VALUE	$ 362,194	$ 388,020
Total debt securities
Contractual maturity:
Maturing in one year or less	113,328	68,347
Maturing after one year through three years	153,707	257,595
Maturing after three years	27,314	24,958
ESTIMATED FAIR VALUE	294,349	350,900
Short-term pooled investments
Contractual maturity:
ESTIMATED FAIR VALUE	$ 67,845	$ 37,120

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

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+ Details