Debt (Bilateral Credit Facilities) (Details) - Line of Credit - Bilateral Credit Facility	Jun. 30, 2019 EUR (€)
Bilateral Credit Facility Expiring in May 2019
Line of Credit Facility
Maximum borrowing capacity	€ 80,000,000.0
Second Bilateral Credit Facility Expiring in May 2019
Line of Credit Facility
Maximum borrowing capacity	80,000,000
Bilateral Credit Facility Expiring in June 2019
Line of Credit Facility
Maximum borrowing capacity	60,000,000.0
Bilateral Credit Facility Expiring in May 2021
Line of Credit Facility
Maximum borrowing capacity	€ 100,000,000.0