Fair Value Measurements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Money Market Funds, at Carrying Value	$ 443,200
Impairment of Intangible Assets, Finite-lived	0	$ 10,039	$ 0
U.K. Composites [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impairment of Intangible Assets, Finite-lived		10,000
Debt(1) | Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	186,060	299,124
Debt(1) | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, Long-term and Short-term, Combined Amount	$ 237,381	$ 325,251