Subsequent events Tables (Details)		3 Months Ended
	Apr. 25, 2018	Mar. 31, 2018	Mar. 31, 2017
Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		4.80	5.40
2018 Euro Term Loan [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage		4.36%
2019 Euro Term Loan [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage		4.19%
2021 Euro Term Loan [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		5
Debt instrument, guarantee fee, stated percentage		4.22%
Net leverage greater than 7.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	6.00%
Net leverage greater than 7.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	6.00%
Net leverage greater than 7.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	6.50%
Net Leverage 7.0x - 6.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	5.00%
Net Leverage 7.0x - 6.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	5.00%
Net Leverage 7.0x - 6.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	5.50%
Net Leverage 6.0x - 5.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	4.25%
Net Leverage 6.0x - 5.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	4.25%
Net Leverage 6.0x - 5.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	4.75%
Net Leverage 5.0x - 4.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.75%
Net Leverage 5.0x - 4.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.75%
Net Leverage 5.0x - 4.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	4.25%
Net Leverage 4.0x - 3.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.25%
Net Leverage 4.0x - 3.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.25%
Net Leverage 4.0x - 3.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.75%
Net Leverage Less Than 3.0x [Member] | 2018 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.25%
Net Leverage Less Than 3.0x [Member] | 2019 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.25%
Net Leverage Less Than 3.0x [Member] | 2021 Euro Term Loan [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.50%
Minimum [Member] | 2021 Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		5
Minimum [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, guarantee fee, stated percentage	3.00%
Minimum [Member] | Net leverage greater than 7.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	7.00
Minimum [Member] | Net leverage greater than 7.0x [Member] | Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		7.00
Minimum [Member] | Net leverage greater than 7.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	7.00
Minimum [Member] | Net Leverage 7.0x - 6.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	6.00
Minimum [Member] | Net Leverage 7.0x - 6.0x [Member] | Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		6.00
Minimum [Member] | Net Leverage 7.0x - 6.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	6.00
Minimum [Member] | Net Leverage 6.0x - 5.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	5.00
Minimum [Member] | Net Leverage 6.0x - 5.0x [Member] | Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		5.00
Minimum [Member] | Net Leverage 6.0x - 5.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	5.00
Minimum [Member] | Net Leverage 5.0x - 4.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	4.00
Minimum [Member] | Net Leverage 5.0x - 4.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	4.00
Minimum [Member] | Net Leverage 4.0x - 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	3.00
Minimum [Member] | Net Leverage 4.0x - 3.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	3.00
Maximum [Member] | 2021 Revolving Credit Facility [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		7
Maximum [Member] | Net Leverage 7.0x - 6.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	7.00
Maximum [Member] | Net Leverage 7.0x - 6.0x [Member] | Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		7.00
Maximum [Member] | Net Leverage 7.0x - 6.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	7.00
Maximum [Member] | Net Leverage 6.0x - 5.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	6.00
Maximum [Member] | Net Leverage 6.0x - 5.0x [Member] | Euro Term Loans [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage		6.00
Maximum [Member] | Net Leverage 6.0x - 5.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	6.00
Maximum [Member] | Net Leverage 5.0x - 4.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	5.00
Maximum [Member] | Net Leverage 5.0x - 4.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	5.00
Maximum [Member] | Net Leverage 4.0x - 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	4.00
Maximum [Member] | Net Leverage 4.0x - 3.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	4.00
Maximum [Member] | Net Leverage Less Than 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	3.00
Maximum [Member] | Net Leverage Less Than 3.0x [Member] | Euro Term Loans [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Financial covenant, net leverage	3.00
Alternative Base Rate [Member] | Net leverage greater than 7.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
Alternative Base Rate [Member] | Net Leverage 7.0x - 6.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	4.25%
Alternative Base Rate [Member] | Net Leverage 6.0x - 5.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	3.50%
Alternative Base Rate [Member] | Net Leverage 5.0x - 4.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	3.00%
Alternative Base Rate [Member] | Net Leverage 4.0x - 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	2.50%
Alternative Base Rate [Member] | Net Leverage Less Than 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	2.25%
Eurodollar [Member] | Net leverage greater than 7.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	6.25%
Eurodollar [Member] | Net Leverage 7.0x - 6.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	5.25%
Eurodollar [Member] | Net Leverage 6.0x - 5.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	4.50%
Eurodollar [Member] | Net Leverage 5.0x - 4.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	4.00%
Eurodollar [Member] | Net Leverage 4.0x - 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	3.50%
Eurodollar [Member] | Net Leverage Less Than 3.0x [Member] | 2021 Revolving Credit Facility [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Debt instrument, interest rate, stated percentage	3.25%