Income Taxes	6 Months Ended
Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company recorded tax provisions of $19.5 million and $34.5 million for the second quarter and the first six months of fiscal year 2018, respectively, representing an effective tax rate of 10% and 9%, respectively. The Company recorded tax provisions of $11.5 million and $30.0 million for the second quarter and the first six months of fiscal year 2017, respectively, representing an effective tax rate of 7% and 8%, respectively. The difference between the U.S. federal statutory tax rate of 35% and the Company’s effective tax rate in all periods was primarily due to income earned in lower tax rate jurisdictions, for which no U.S. income tax has been provided, as the Company intends to permanently reinvest these earnings outside of the U.S. The Company’s total gross unrecognized tax benefits as of September 30, 2017 increased by $90.6 million in the first six months of fiscal year 2018 to $121.0 million. The increase is primarily attributable to an additional deduction claimed on federal and state amended returns for repurchase premium paid in connection with the early redemption of the Company’s 3.125% Junior Convertible debenture due March 15, 2037 (2037 Convertible Notes) in fiscal year 2014. As of September 30, 2017, the total amount of unrecognized tax benefits that, if realized in a future period, would favorably affect the effective tax rate is $13.7 million. Another $85.5 million related to the 2037 Convertible Notes would increase additional paid-in capital. It is reasonably possible that changes to our unrecognized tax benefits could be significant in the next twelve months due to tax audit settlements and lapses of statutes of limitation. As a result of uncertainties regarding tax audit settlements and their possible outcomes, an estimate of the range of increase or decrease that could occur in the next twelve months cannot be determined at this time. The Company’s policy is to include interest and penalties related to income tax liabilities within the provision for income taxes on the condensed consolidated statements of income. The balance of accrued interest and penalties recorded in the condensed consolidated balance sheets and the amounts of interest and penalties included in the Company's provision for income taxes were not material for all periods presented. The Company is no longer subject to U.S. federal audits by taxing authorities for years through fiscal year 2013, U.S. state audits for years through fiscal year 2010 and tax audits in Ireland for years through fiscal year 2011.

Income Taxes

The Company recorded tax provisions of $19.5 million and $34.5 million for the second quarter and the first six months of fiscal year 2018, respectively, representing an effective tax rate of 10% and 9%, respectively. The Company recorded tax provisions of $11.5 million and $30.0 million for the second quarter and the first six months of fiscal year 2017, respectively, representing an effective tax rate of 7% and 8%, respectively.

The difference between the U.S. federal statutory tax rate of 35% and the Company’s effective tax rate in all periods was primarily due to income earned in lower tax rate jurisdictions, for which no U.S. income tax has been provided, as the Company intends to permanently reinvest these earnings outside of the U.S.

The Company’s total gross unrecognized tax benefits as of September 30, 2017 increased by $90.6 million in the first six months of fiscal year 2018 to $121.0 million. The increase is primarily attributable to an additional deduction claimed on federal and state amended returns for repurchase premium paid in connection with the early redemption of the Company’s 3.125% Junior Convertible debenture due March 15, 2037 (2037 Convertible Notes) in fiscal year 2014. As of September 30, 2017, the total amount of unrecognized tax benefits that, if realized in a future period, would favorably affect the effective tax rate is $13.7 million. Another $85.5 million related to the 2037 Convertible Notes would increase additional paid-in capital. It is reasonably possible that changes to our unrecognized tax benefits could be significant in the next twelve months due to tax audit settlements and lapses of statutes of limitation. As a result of uncertainties regarding tax audit settlements and their possible outcomes, an estimate of the range of increase or decrease that could occur in the next twelve months cannot be determined at this time.

The Company’s policy is to include interest and penalties related to income tax liabilities within the provision for income taxes on the condensed consolidated statements of income. The balance of accrued interest and penalties recorded in the condensed consolidated balance sheets and the amounts of interest and penalties included in the Company's provision for income taxes were not material for all periods presented.

The Company is no longer subject to U.S. federal audits by taxing authorities for years through fiscal year 2013, U.S. state audits for years through fiscal year 2010 and tax audits in Ireland for years through fiscal year 2011.