Fair Value Measurements Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Defined Benefit Plan, Benefit Obligation	$ 4,881	$ 5,033	$ 4,264
Assets, Fair Value Disclosure		55
Financial and Nonfinancial Liabilities, Fair Value Disclosure	333	4
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible Debt, Fair Value Disclosures	136,500	129,900
Other Debts, excluding capital leases	19,700	21,800
Assets, Fair Value Disclosure		33
Financial and Nonfinancial Liabilities, Fair Value Disclosure	333	4
TVN Voluntary Departure Plan [Member] | TVN [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Postemployment Benefits Liability	2,400	5,100
Fair Value, Measurements, Nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	0	0	0
Financial and Nonfinancial Liabilities, Fair Value Disclosure	$ 0	$ 0	$ 0