Available-for-Sale Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Amortized Cost Basis	$ 500,000
Available-for-sale Securities, Debt Maturities, Next Rolling Twelve Months, Fair Value	500,044
Available-for-sale Debt Securities, Amortized Cost Basis	500,000
Available-for-sale Securities, Gross Unrealized Gains	44
Available-for-sale Securities, Gross Unrealized Losses	0
Available-for-sale Securities, Debt Securities	500,044	0
Fixed-rate [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	500,000
Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	500,000
Available-for-sale Securities, Gross Unrealized Gains	44
Available-for-sale Securities, Gross Unrealized Losses	0
Available-for-sale Securities, Debt Securities	$ 500,044

Amount of debt securities categorized neither as held-to-maturity nor trading.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

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+ Details

- Definition

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.

+ References+ Details