Debt (Bilateral Credit Facilities) (Details) - Line of Credit - Bilateral credit facilities - EUR (€)	Dec. 31, 2017	Sep. 30, 2017
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	€ 340,000,000
Bilateral credit facility expiring in May 2019, tranche one
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	80,000,000
Bilateral credit facility expiring in May 2019, tranche two
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity		€ 80,000,000
Bilateral credit facility expiring in June 2019
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	80,000,000
Bilateral credit facility expiring in May 2021
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	€ 100,000,000