Financing Arrangements (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt, gross	$ 183,118	$ 183,636
Unamortized discount and debt issuance costs	(22,643)	(27,368)
Long-term debt	160,475	156,268
Long-term debt, current maturities, gross	(1,518)	(83,636)
Unamortized discount and debt issuance costs, current	0	268
Long-term debt, current maturities	1,518	83,368
Long-term debt, excluding current maturities, gross	181,600	100,000
Unamortized discount and debt issuance costs, noncurrent	(22,643)	(27,100)
Long-term debt, excluding current maturities	158,957	72,900
Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt		83,300
Other Debt [Member]
Debt Instrument [Line Items]
Long-term debt, gross	1,518	380
Long-term debt	1,518	380
Senior notes [Member] | Convertible Notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt, gross	0	83,256
Unamortized discount and debt issuance costs	0	(268)
Long-term debt	0	82,988
Senior notes [Member] | Convertible Notes due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross	100,000	100,000
Unamortized discount and debt issuance costs	(22,643)	(27,100)
Long-term debt	77,357	72,900
Revolving Credit Facility [Member] | ABL Facility [Member]
Debt Instrument [Line Items]
Long-term debt, gross	81,600	0
Long-term debt	$ 81,600	$ 0