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Fair Value Measurements - Narratives (Details) - USD ($) $ in Thousands	Jun. 26, 2020	Dec. 31, 2019	Sep. 27, 2019	Dec. 31, 2015
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Long-term Debt	$ 20,300	$ 17,200
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	$ 200	800
Convertible Note due 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.375%		4.375%
Convertible Note due 2022 \| Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Fair Value Disclosures	$ 40,100
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	$ 8,000	66,800
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%		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	$ 102,900	$ 131,900