Lines of Credit and Long-Term Debt - Components of Interest Expense (Details) - 3.5% Convertible Notes Due 2023 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Cash interest expense	$ 7,000	$ 3,462
Non-cash interest expense	9,459	4,378
Total interest expense	$ 16,459	$ 7,840