Fair Value Measurements - Narrative (Details) - USD ($) |
3 Months Ended | ||
|---|---|---|---|
Mar. 30, 2018 |
Dec. 31, 2017 |
Jun. 08, 2015 |
|
| Debt Instrument [Line Items] | |||
| Cost method investments, fair value | $ 12,600,000 | $ 12,600,000 | |
| 1.00% Notes | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, interest rate (as a percent) | 1.00% | ||
| Convertible Debt | 1.00% Notes | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, interest rate (as a percent) | 1.00% | 1.00% | |
| Convertible Debt | 1.625% Notes | |||
| Debt Instrument [Line Items] | |||
| Debt instrument, interest rate (as a percent) | 1.625% | ||
| AXSEM | |||
| Debt Instrument [Line Items] | |||
| Contingent consideration relating to the second earn-out | $ 0 |