Commitments - Purchase Commitments (Details) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Purchase Commitments | ||
| Commitments to suppliers for inventory purchases | $ 7.1 | $ 9.0 |
| Medtronic | ||
| Purchase Commitments | ||
| Commitments to suppliers for inventory purchases | $ 0.0 | $ 0.4 |