Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Assets:
Financial assets at fair value	$ 365,392
Corporate bonds [Member]
Assets:
Financial assets at fair value	171,405
Asset-backed securities [Member]
Assets:
Financial assets at fair value	65,319
Agency bonds [Member]
Assets:
Financial assets at fair value	39,278
Treasury bills [Member]
Assets:
Financial assets at fair value	33,727
Municipal bonds [Member]
Assets:
Financial assets at fair value	29,571
Sovereign bonds [Member]
Assets:
Financial assets at fair value	11,823
Covered bonds [Member]
Assets:
Financial assets at fair value	11,271
Commercial paper [Member]
Assets:
Financial assets at fair value	2,998
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	9,398
Money market instruments	1,069
Corporate stock	1,763
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate bonds [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Asset-backed securities [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency bonds [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Treasury bills [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal bonds [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Sovereign bonds [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Covered bonds [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Commercial paper [Member]
Assets:
Financial assets at fair value
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Fair Value, Measurements, Recurring [Member] \| Currency Forward Contract [Member]
Assets:
Currency forward contracts	1
Liabilities:
Currency forward contracts	83
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents
Money market instruments
Corporate stock
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Corporate bonds [Member]
Assets:
Financial assets at fair value	171,405
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Asset-backed securities [Member]
Assets:
Financial assets at fair value	65,319
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Agency bonds [Member]
Assets:
Financial assets at fair value	39,278
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Treasury bills [Member]
Assets:
Financial assets at fair value	33,727
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Municipal bonds [Member]
Assets:
Financial assets at fair value	29,571
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Sovereign bonds [Member]
Assets:
Financial assets at fair value	11,823
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Covered bonds [Member]
Assets:
Financial assets at fair value	11,271
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Commercial paper [Member]
Assets:
Financial assets at fair value	2,998
Significant Other Observable Inputs (Level 2) [Member] \| Fair Value, Measurements, Recurring [Member] \| Currency Forward Contract [Member]
Assets:
Currency forward contracts
Liabilities:
Currency forward contracts

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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

-Publisher FASB

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

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-Name Statement of Financial Accounting Standard (FAS)

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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 5: http://www.xbrl.org/2003/role/presentationRef

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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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 element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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