Fair Value Measurements - Narratives (Details) - USD ($) $ in Thousands	Sep. 27, 2019	Dec. 31, 2018	Dec. 31, 2015
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Debts, Excluding Finance Leases	$ 17,300	$ 19,700
Fair Value, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets measured and recorded at fair value	0
Total liabilities 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, Current	1,100
Postemployment Benefits Liability		2,400
Other Debts, Excluding Finance Leases	$ 17,262
Convertible Note due 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.00%		4.00%
Convertible Note due 2020 | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Fair Value Disclosures	$ 60,300	$ 136,500
Convertible Note due 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.00%
Convertible Note due 2024 | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Fair Value Disclosures	$ 120,000