Credit facility (Details) (USD $)	12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013	Jun. 27, 2013	Feb. 04, 2015
Line of Credit Facility [Line Items]
Interest Expense	$ 62,034,000	$ 48,716,000	$ 40,915,000
Credit Agreement Maturity June 27, 2018 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				2,000,000,000.0
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					2,555,000,000.000
Line of Credit Facility Increase Option					300,000,000
Debt Instrument, Description of Variable Rate Basis	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%
Interest Expense	19,900,000	14,600,000	7,000,000
Short-term Debt, Weighted Average Interest Rate	1.68%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Period For Leverage Ratio To Determine Interest Rate Spread	preceding four fiscal quarters
Debt Instrument Interest Rate Spread On Overdue Principal In Event Of Default					2.00%
Debt Instrument Interest Rate Spread On Overdue Amounts In Event Of Default					2.00%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Description of Variable Rate Basis	adjusted LIBOR rate (based on one, two, three, or six-month interest periods)
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	461,900,000.0
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					125,000,000
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					25,000,000
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Line of Credit Facility Swingline Loan Sublimit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					$ 25,000,000