Credit facility (Details)	3 Months Ended		6 Months Ended
	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Mar. 31, 2016 USD ($)	Feb. 04, 2015 USD ($)	Jun. 27, 2013 USD ($)
Line of Credit Facility [Line Items]
Debt Issuance Costs	$ 7,700,000		$ 7,700,000		$ 8,800,000
Interest expense	35,126,000	$ 25,644,000	69,542,000	$ 49,696,000
Credit Agreement Maturity June 27, 2018 [Member]
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount							$ 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]
Credit agreement maximum borrowing amount						$ 2,555,000,000.000
Increase option amount						$ 249,400,000.0	$ 300,000,000
Interest expense	$ 12,000,000	$ 4,900,000	$ 23,600,000	$ 8,500,000
Short-term Debt, Weighted Average Interest Rate	2.55%		2.55%
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]
Amount of credit agreement borrowings outstanding	$ 1,678,000,000		$ 1,678,000,000		$ 1,052,000,000
Period for leverage ratio to determine interest rate spread			preceding four fiscal quarters
Interest rate spread on overdue principal in event of default (percentage)						2.00%
Interest rate spread on overdue amounts in event of default (percentage)						2.00%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [Member] | Debt Instrument Interest Rate Option1 [Member]
Line of Credit Facility [Line Items]
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%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [Member] | Debt Instrument Interest Rate Option1 [Member] | Minimum
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			0.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [Member] | Debt Instrument Interest Rate Option1 [Member] | Maximum
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			1.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [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] | Revolving credit facility [Member] | Debt Instrument Interest Rate Option 2 [Member] | Minimum
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			1.25%
February 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [Member] | Debt Instrument Interest Rate Option 2 [Member] | Maximum
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			2.25%
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]
Credit agreement maximum borrowing amount						$ 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]
Credit agreement maximum borrowing amount						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]
Credit agreement maximum borrowing amount						$ 25,000,000
December 2015 Amended Credit Facility with Maturity Dates of June 2018 and February 2020 [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit agreement maximum borrowing amount	2,774,000,000.000		$ 2,774,000,000.000
Increase option amount	219,000,000		219,000,000
Remaining Increase Option Amount	$ 30,400,000		$ 30,400,000
Credit Agreement, Total Leverage Ratio, Temporary Maximum Allowed, First Four Quarters	5.00		5.00
Credit Agreement, Total Leverage Ratio, Temporary Maximum Allowed, Next Three Quarters	4.75		4.75
Credit Agreement, Total Leverage Ratio, Maximum	4.50		4.50