Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets:
Money market instruments	$ 460	$ 5,076
Financial assets at fair value	374,273
Corporate Bonds [Member]
Assets:
Financial assets at fair value	190,166
Asset-Backed Securities [Member]
Assets:
Financial assets at fair value	68,176
Treasury Bills [Member]
Assets:
Financial assets at fair value	52,415
Sovereign Bonds [Member]
Assets:
Financial assets at fair value	30,435
Municipal Bonds [Member]
Assets:
Financial assets at fair value	28,583
Commercial Paper [Member]
Assets:
Financial assets at fair value	3,000
Agency Bonds [Member]
Assets:
Financial assets at fair value	1,498
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	12,947
Corporate stock	1,669
Money market instruments	460
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] | 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] | 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] | 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] | 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] | 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] | Currency Forward Contract [Member]
Assets:
Currency forward contracts
Liabilities:
Currency forward contracts
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents
Corporate stock
Money market instruments
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Bonds [Member]
Assets:
Financial assets at fair value	190,166
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Asset-Backed Securities [Member]
Assets:
Financial assets at fair value	68,176
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Treasury Bills [Member]
Assets:
Financial assets at fair value	52,415
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Sovereign Bonds [Member]
Assets:
Financial assets at fair value	30,435
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Municipal Bonds [Member]
Assets:
Financial assets at fair value	28,583
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Assets:
Financial assets at fair value	3,000
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Agency Bonds [Member]
Assets:
Financial assets at fair value	1,498
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Currency Forward Contract [Member]
Assets:
Currency forward contracts	61
Liabilities:
Currency forward contracts	$ 11