Credit facility (Notes)	9 Months Ended
Dec. 31, 2016
Line of Credit Facility [Abstract]
Credit Facility	Credit Facility In February 2015, the Company amended its existing $2.0 billion credit agreement by increasing the revolving credit facility to $2.555 billion and removing the term loan portion of the agreement. The new credit agreement includes two tranches. One tranche consists of bank commitments through February 2020 and another tranche consists of bank commitments through June 2018, the maturity date of the original credit agreement. The increase option permitting the Company, subject to certain requirements, to arrange with existing lenders or new lenders to provide up to an aggregate of $300 million in additional commitments, was also adjusted to $249.4 million. The credit agreement provides for a $125 million foreign currency sublimit, a $25 million letter of credit sublimit and a $25 million swingline loan sublimit. The amended credit agreement was accounted for as a modification and as such any remaining unamortized deferred costs associated with the prior credit agreement was associated with the new agreement since the borrowing capacity was increased. At December 31, 2016, $1.683 billion of revolving credit facility borrowings were outstanding under the credit agreement compared to $1.052 billion at March 31, 2016. The carrying values reflected in the Company's condensed consolidated balance sheets as of December 31, 2016 and March 31, 2016 have been reduced by debt issuance costs of $7.1 million and $8.8 million, respectively. In December 2015, the Company secured additional revolving credit commitments of $219 million from various banks in the February 2020 tranche under the increase option of the credit agreement, bringing its revolving credit facility to $2.774 billion. The remaining increase option was $30.4 million as of December 31, 2016. In December 2015, the Company amended the maximum total leverage ratio in Section 6.11 of its existing credit agreement to allow the Total Leverage Ratio (as defined in that agreement) to be temporarily increased to 5.00 to 1.00 for a period of four consecutive quarters in conjunction with a permitted acquisition occurring during the first of the four quarters. The Total Leverage Ratio then decreases to 4.75 to 1.00 for three consecutive quarters, finally returning to the stated 4.50 to 1.00 Total Leverage Ratio of the credit agreement after a period of seven consecutive fiscal periods. The Company can elect to use this special feature, also referred to as an Adjusted Covenant Period, no more than two times during the term of the credit agreement and also can terminate an Adjusted Covenant Period earlier than the seven consecutive quarters allowed. The Company elected to use this feature in conjunction with its acquisition of Atmel during the quarter ended June 30, 2016. The loans under the credit agreement bear interest, at the Company's option, at the base rate plus a spread of 0.25% to 1.25% or an adjusted LIBOR rate (based on one, two, three, or six-month interest periods) plus a spread of 1.25% to 2.25%, in each case with such spread being determined based on the consolidated leverage ratio for the preceding four fiscal quarters (in the case of the 2018 tranche revolving loans) or the consolidated senior leverage ratio (in the case of the 2020 tranche revolving loans). The base rate means the highest of JPMorgan Chase Bank, N.A.'s prime rate, the federal funds rate plus a margin equal to 0.50% and the adjusted LIBOR rate for a 1-month interest period plus a margin equal to 1.00%. Swingline loans accrue interest at a per annum rate based on the base rate plus the applicable margin for base rate loans. Base rate loans may only be made in U.S. Dollars. The Company is also obligated to pay other customary administration fees and letter of credit fees for a credit facility of this size and type. Interest is due and payable in arrears quarterly for loans bearing interest at the base rate and at the end of an interest period (or at each three-month interval in the case of loans with interest periods greater than three months) in the case of loans bearing interest at the adjusted LIBOR rate. Interest expense related to the credit agreement was approximately $11.9 million and $35.5 million in the three and nine months ended December 31, 2016, respectively, and $6.4 million and $14.9 million for the three and nine months ended December 31, 2015, respectively. Principal, together with all accrued and unpaid interest, is due and payable on the respective tranche maturity date, which is June 27, 2018 and February 4, 2020. The weighted average interest rate on borrowings outstanding at December 31, 2016 related to the credit agreement was 2.49%. The Company also pays a quarterly commitment fee on the available but unused portion of its line of credit which is calculated on the average daily available balance during the period. The Company may prepay the loans and terminate the commitments, in whole or in part, at any time without premium or penalty, subject to certain conditions including minimum amounts in the case of commitment reductions and reimbursement of certain costs in the case of prepayments of LIBOR loans. The Company's obligations under the credit agreement are guaranteed by certain of its subsidiaries meeting materiality thresholds set forth in the credit agreement. To secure the Company's obligations under the credit agreement, the Company and its domestic subsidiaries are required to pledge the equity securities of certain of their respective material subsidiaries, subject to certain exceptions and limitations. The credit agreement contains customary affirmative and negative covenants, including covenants that limit or restrict the Company and its subsidiaries' ability to, among other things, incur subsidiary indebtedness, grant liens, merge or consolidate, dispose of assets, make investments, make acquisitions, enter into certain transactions with affiliates, pay dividends or make distributions, repurchase stock, enter into restrictive agreements and enter into sale and leaseback transactions, in each case subject to customary exceptions for a credit facility of this size and type. The Company is also required to maintain compliance with consolidated senior and total leverage ratios and a consolidated interest coverage ratio. At December 31, 2016, the Company was in compliance with these covenants. The credit agreement includes customary events of default that include, among other things, non-payment defaults, inaccuracy of representations and warranties, covenant defaults, cross default to material indebtedness, bankruptcy and insolvency defaults, material judgment defaults, ERISA defaults and a change of control default. The occurrence of an event of default could result in the acceleration of the obligations under the credit agreement. Under certain circumstances, a default interest rate will apply on all obligations during the existence of an event of default under the credit agreement at a per annum rate equal to 2.00% above the applicable interest rate for any overdue principal and 2.00% above the rate applicable for base rate loans for any other overdue amounts.

Credit Facility

In February 2015, the Company amended its existing $2.0 billion credit agreement by increasing the revolving credit facility to $2.555 billion and removing the term loan portion of the agreement. The new credit agreement includes two tranches. One tranche consists of bank commitments through February 2020 and another tranche consists of bank commitments through June 2018, the maturity date of the original credit agreement. The increase option permitting the Company, subject to certain requirements, to arrange with existing lenders or new lenders to provide up to an aggregate of $300 million in additional commitments, was also adjusted to $249.4 million. The credit agreement provides for a $125 million foreign currency sublimit, a $25 million letter of credit sublimit and a $25 million swingline loan sublimit. The amended credit agreement was accounted for as a modification and as such any remaining unamortized deferred costs associated with the prior credit agreement was associated with the new agreement since the borrowing capacity was increased. At December 31, 2016, $1.683 billion of revolving credit facility borrowings were outstanding under the credit agreement compared to $1.052 billion at March 31, 2016. The carrying values reflected in the Company's condensed consolidated balance sheets as of December 31, 2016 and March 31, 2016 have been reduced by debt issuance costs of $7.1 million and $8.8 million, respectively.

In December 2015, the Company secured additional revolving credit commitments of $219 million from various banks in the February 2020 tranche under the increase option of the credit agreement, bringing its revolving credit facility to $2.774 billion. The remaining increase option was $30.4 million as of December 31, 2016.

In December 2015, the Company amended the maximum total leverage ratio in Section 6.11 of its existing credit agreement to allow the Total Leverage Ratio (as defined in that agreement) to be temporarily increased to 5.00 to 1.00 for a period of four consecutive quarters in conjunction with a permitted acquisition occurring during the first of the four quarters.

The Total Leverage Ratio then decreases to 4.75 to 1.00 for three consecutive quarters, finally returning to the stated 4.50 to 1.00 Total Leverage Ratio of the credit agreement after a period of seven consecutive fiscal periods. The Company can elect to use this special feature, also referred to as an Adjusted Covenant Period, no more than two times during the term of the credit agreement and also can terminate an Adjusted Covenant Period earlier than the seven consecutive quarters allowed. The Company elected to use this feature in conjunction with its acquisition of Atmel during the quarter ended June 30, 2016.

The loans under the credit agreement bear interest, at the Company's option, at the base rate plus a spread of 0.25% to 1.25% or an adjusted LIBOR rate (based on one, two, three, or six-month interest periods) plus a spread of 1.25% to 2.25%, in each case with such spread being determined based on the consolidated leverage ratio for the preceding four fiscal quarters (in the case of the 2018 tranche revolving loans) or the consolidated senior leverage ratio (in the case of the 2020 tranche revolving loans). The base rate means the highest of JPMorgan Chase Bank, N.A.'s prime rate, the federal funds rate plus a margin equal to 0.50% and the adjusted LIBOR rate for a 1-month interest period plus a margin equal to 1.00%. Swingline loans accrue interest at a per annum rate based on the base rate plus the applicable margin for base rate loans. Base rate loans may only be made in U.S. Dollars. The Company is also obligated to pay other customary administration fees and letter of credit fees for a credit facility of this size and type.

Interest is due and payable in arrears quarterly for loans bearing interest at the base rate and at the end of an interest period (or at each three-month interval in the case of loans with interest periods greater than three months) in the case of loans bearing interest at the adjusted LIBOR rate. Interest expense related to the credit agreement was approximately $11.9 million and $35.5 million in the three and nine months ended December 31, 2016, respectively, and $6.4 million and $14.9 million for the three and nine months ended December 31, 2015, respectively. Principal, together with all accrued and unpaid interest, is due and payable on the respective tranche maturity date, which is June 27, 2018 and February 4, 2020. The weighted average interest rate on borrowings outstanding at December 31, 2016 related to the credit agreement was 2.49%. The Company also pays a quarterly commitment fee on the available but unused portion of its line of credit which is calculated on the average daily available balance during the period. The Company may prepay the loans and terminate the commitments, in whole or in part, at any time without premium or penalty, subject to certain conditions including minimum amounts in the case of commitment reductions and reimbursement of certain costs in the case of prepayments of LIBOR loans.

The Company's obligations under the credit agreement are guaranteed by certain of its subsidiaries meeting materiality thresholds set forth in the credit agreement. To secure the Company's obligations under the credit agreement, the Company and its domestic subsidiaries are required to pledge the equity securities of certain of their respective material subsidiaries, subject to certain exceptions and limitations.

The credit agreement contains customary affirmative and negative covenants, including covenants that limit or restrict the Company and its subsidiaries' ability to, among other things, incur subsidiary indebtedness, grant liens, merge or consolidate, dispose of assets, make investments, make acquisitions, enter into certain transactions with affiliates, pay dividends or make distributions, repurchase stock, enter into restrictive agreements and enter into sale and leaseback transactions, in each case subject to customary exceptions for a credit facility of this size and type. The Company is also required to maintain compliance with consolidated senior and total leverage ratios and a consolidated interest coverage ratio. At December 31, 2016, the Company was in compliance with these covenants.

The credit agreement includes customary events of default that include, among other things, non-payment defaults, inaccuracy of representations and warranties, covenant defaults, cross default to material indebtedness, bankruptcy and insolvency defaults, material judgment defaults, ERISA defaults and a change of control default. The occurrence of an event of default could result in the acceleration of the obligations under the credit agreement. Under certain circumstances, a default interest rate will apply on all obligations during the existence of an event of default under the credit agreement at a per annum rate equal to 2.00% above the applicable interest rate for any overdue principal and 2.00% above the rate applicable for base rate loans for any other overdue amounts.