Fair Value of Financial Assets and Liabilities - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2013 Security	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Number of Auction Rate Securities With Underlying Loans Which Have No Guarantees	2
Investment Holding Period	5 years
Auction rate securities that have partial guarantees by the U.S. government, market value	$ 16,000,000
Discount rate used to estimate fair value of investments	1.00%
The rate used for the discount margin to determine the estimated fair value of investment in auction rate securities	1.00%
Percentage of Loans Guaranteed	95.00%
Short term investment	1,223,463,000	1,421,710,000
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Coupon rate used to estimate fair value of invesments - Start Range	0.00%
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Coupon rate used to estimate fair value of invesments - End Range	5.00%
US Government Agencies Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	2,085,086,000	2,200,215,000
US Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	1,520,806,000	1,489,706,000
High Yield Corporate Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	529,059,000	519,222,000
Municipal Obligations
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	971,293,000	1,034,787,000
Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	6,593,684,000	6,595,090,000
Foreign Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	1,415,463,000	1,278,862,000
Average credit rating	A+
Foreign Sovereign Debt Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Average credit rating	AA+
Percentage of Available For Sale Securities Debt Securities	5.00%
Auction Rate Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale Securities	$ 68,247,000	$ 70,180,000
Average credit rating	AA
LenovoEMC
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Discount rate used to estimate fair value of investments	6.00%

Auction rate securities, at Fair Value

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Description of the average credit rating indicative of likelihood of repayment of debt instruments given by credit rating agencies (for example, Standard and Poor's, Moody's, Fitch).

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- Definition

Financial Instruments Fair Value Assumptions Weighted Average Discount Rate

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Investment Holding Period

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- Definition

The highest interest rate in the aggregated short-tem debt instruments.

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The lowest interest rate in the aggregated short-tem debt instruments.

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Number of Auction Rate Securities With Underlying Loans Which Have No Guarantees

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- Definition

Percentage of Loans Guaranteed

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- Definition

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

+ References

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

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