Fair Value of Financial Instruments - Financial Assets and Liabilities Carried at Fair Value (Detail) - USD ($) $ in Millions | Apr. 30, 2017 | Apr. 30, 2016 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total financial assets, Fair Value | | $ 170.9 | $ 55.4 |
Total financial liabilities, Fair Value | | 16.1 | 17.3 |
Other assets, net [Member] | Marketable securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [1] | 36.9 | 34.2 |
Short-term Investments [Member] | Bank Time Deposits [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [2] | 121.2 | 10.3 |
Prepaid Expenses and Other Current Assets [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 3.9 | 9.2 |
Prepaid Expenses and Other Current Assets [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0.5 | 0.9 |
Prepaid Expenses and Other Current Assets [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 6.6 | 0.6 |
Prepaid Expenses and Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 1.8 | 0.2 |
Accounts Payable and Accrued Liabilities [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 5.7 | |
Accounts Payable and Accrued Liabilities [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0.4 | 0.5 |
Accounts Payable and Accrued Liabilities [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 1.7 | 14.8 |
Accounts Payable and Accrued Liabilities [Member] | Currency Swap [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 7.9 | |
Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0.4 | 2 |
Level 1 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total financial assets, Fair Value | | 158.1 | 44.5 |
Total financial liabilities, Fair Value | | 0 | 0 |
Level 1 [Member] | Other assets, net [Member] | Marketable securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [1] | 36.9 | 34.2 |
Level 1 [Member] | Short-term Investments [Member] | Bank Time Deposits [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [2] | 121.2 | 10.3 |
Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 1 [Member] | Prepaid Expenses and Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 1 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | |
Level 1 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | 0 |
Level 1 [Member] | Accounts Payable and Accrued Liabilities [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | 0 |
Level 1 [Member] | Accounts Payable and Accrued Liabilities [Member] | Currency Swap [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | |
Level 1 [Member] | Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | 0 |
Level 2 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total financial assets, Fair Value | | 12.8 | 10.9 |
Total financial liabilities, Fair Value | | 16.1 | 17.3 |
Level 2 [Member] | Other assets, net [Member] | Marketable securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [1] | 0 | 0 |
Level 2 [Member] | Short-term Investments [Member] | Bank Time Deposits [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [2] | 0 | 0 |
Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 3.9 | 9.2 |
Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0.5 | 0.9 |
Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 6.6 | 0.6 |
Level 2 [Member] | Prepaid Expenses and Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 1.8 | 0.2 |
Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 5.7 | |
Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0.4 | 0.5 |
Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 1.7 | 14.8 |
Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member] | Currency Swap [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 7.9 | |
Level 2 [Member] | Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0.4 | 2 |
Level 3 [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Total financial assets, Fair Value | | 0 | 0 |
Total financial liabilities, Fair Value | | 0 | 0 |
Level 3 [Member] | Other assets, net [Member] | Marketable securities [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [1] | 0 | 0 |
Level 3 [Member] | Short-term Investments [Member] | Bank Time Deposits [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Financial Assets, Fair Value | [2] | 0 | 0 |
Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 3 [Member] | Prepaid Expenses and Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Assets, Fair Value | [3] | 0 | 0 |
Level 3 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Forward Contracts [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | |
Level 3 [Member] | Accounts Payable and Accrued Liabilities [Member] | Precious Metal Collars [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | 0 |
Level 3 [Member] | Accounts Payable and Accrued Liabilities [Member] | Foreign Exchange Contract [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | 0 |
Level 3 [Member] | Accounts Payable and Accrued Liabilities [Member] | Currency Swap [Member] | Cash Flow Hedging [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | 0 | |
Level 3 [Member] | Accounts Payable and Accrued Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Foreign Exchange Contract [Member] | | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | | |
Derivative Liability, Fair Value | [4] | $ 0 | $ 0 |
| |
[1] | Included within Other assets, net. | |
[2] | Included within Short-term investments. | |
[3] | Included within Prepaid expenses and other current assets or Other assets, net evaluated based on the maturity of the contract. | |
[4] | Included within Accounts payable and accrued liabilities or Other long-term liabilities evaluated based on the maturity of the contract. | |