Long-Term Debt Schedule of Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Feb. 16, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total carrying value of debt	$ 111,838		$ 267
Less: current maturities	(114)		(111)
Long-term debt, less current portion	111,724		156
Senior Notes [Member]
Debt Instrument [Line Items]
Less: debt discount and issuance costs, net	(32,232)		0
Total carrying value of debt	111,518		0
Equity component of exchangeable notes, net of issuance costs	26,699		0
Other Long-Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt	320		267
4.50% Exchangeable Senior Notes Due 2023 [Member]
Debt Instrument [Line Items]
Less: debt discount and issuance costs, net	$ 6,190
Debt instrument, interest rate, stated percentage	4.50%	4.50%
4.50% Exchangeable Senior Notes Due 2023 [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 143,750		$ 0