Fair Value Measurements - Narratives (Details) - USD ($) $ in Thousands	Jun. 28, 2019	Dec. 31, 2018
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Fair Value Disclosures	$ 150,000	$ 136,500
Other Debts, Excluding Finance Leases	18,000	19,700
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total liabilities measured and recorded at fair value	0
Total assets measured and recorded at fair value	0
TVN [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Postemployment Benefits Liability	1,400	$ 2,400
Other Debts, Excluding Finance Leases	$ 17,977