Credit facility (Details) (USD $)	3 Months Ended		6 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Jun. 27, 2013
Line of Credit Facility [Line Items]
Interest expense	$ 14,019,000	$ 12,354,000	$ 27,697,000	$ 24,210,000
Credit Agreement Maturity June 27, 2018 [Member]
Line of Credit Facility [Line Items]
Initiation date			Jun. 27, 2013
Credit agreement					2,000,000,000.0
Maturity Date			Jun. 27, 2018
Increase option amount					300,000,000
Line of Credit Facility, Fair Value of Amount Outstanding	965,600,000.0		965,600,000.0
Debt discount	1,000,000		1,000,000
Interest expense	5,100,000	4,000,000	10,100,000	7,500,000
Short-term Debt, Weighted Average Interest Rate	1.65%		1.65%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member]
Line of Credit Facility [Line Items]
Period for leverage ratio to determine interest rate spread			preceding four fiscal quarter period
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%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member]
Line of Credit Facility [Line Items]
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%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			0.25%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option1 [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			1.25%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member]
Line of Credit Facility [Line Items]
Description of variable rate basis			adjusted LIBOR rate (based on one, two, three, or six-month interest periods)
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			1.25%
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit [Member] | Debt Instrument Interest Rate Option 2 [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Spread on variable rate (percentage)			2.25%
Credit Agreement Maturity June 27, 2018 [Member] | Term loan [Member]
Line of Credit Facility [Line Items]
Credit agreement					350,000,000
Line of Credit Facility, Fair Value of Amount Outstanding	341,200,000		341,200,000
Credit Agreement Maturity June 27, 2018 [Member] | Revolving credit facility [Member]
Line of Credit Facility [Line Items]
Credit agreement					1,650,000,000.00
Line of Credit Facility, Fair Value of Amount Outstanding	624,400,000		624,400,000
Credit Agreement Maturity June 27, 2018 [Member] | Foreign Line of Credit [Member]
Line of Credit Facility [Line Items]
Credit agreement					125,000,000
Credit Agreement Maturity June 27, 2018 [Member] | Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Credit agreement					35,000,000
Credit Agreement Maturity June 27, 2018 [Member] | Line of Credit Facility Swingline Loan Sublimit [Member]
Line of Credit Facility [Line Items]
Credit agreement					$ 25,000,000