Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) | Sep. 30, 2014 | Dec. 31, 2013 |
In Millions, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | $217.80 | $101 |
Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 251.3 | 150.2 |
Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | -33.5 | -49.2 |
Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 179.7 | 145.8 |
Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 20.4 | 34.9 |
Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 8.3 | 11 |
Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 15.5 | 5 |
Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 0.8 | 7.5 |
Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 134.7 | 87.4 |
Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 14.7 | 4.4 |
Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 56.9 | ' |
Quoted Prices in Active Markets for Identical Assets (Level 1) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 18.6 | 11 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 43.4 | 50.3 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | -24.8 | -39.3 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 28.7 | 45.9 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 20.4 | 34.9 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 8.3 | 11 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 14.7 | 4.4 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | ' |
Significant Other Observable Inputs (Level 2) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 199.2 | 90 |
Significant Other Observable Inputs (Level 2) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 207.9 | 99.9 |
Significant Other Observable Inputs (Level 2) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | -8.7 | -9.9 |
Significant Other Observable Inputs (Level 2) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 151 | 99.9 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 15.5 | 5 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0.8 | 7.5 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 134.7 | 87.4 |
Significant Other Observable Inputs (Level 2) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 56.9 | ' |
Significant Unobservable Inputs (Level 3) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | $0 | ' |