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Earnings per Share Basis and Diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net income	$ (12,760)	$ (15,786)	$ (16,844)	$ (18,856)	$ (16,980)	$ (21,226)	$ (19,513)	$ (20,207)	$ (64,246)	$ (77,926)	$ (75,225)
Denominator
Weighted average shares (basic)									34,465	31,627	30,395
Dilutive effect of potential common shares									0	0	0
Weighted Average Number of Shares Outstanding, Basic and Diluted									34,465	31,627	30,395
Weighted Average Number of Shares Outstanding, Diluted									34,465	31,627	30,395
Basic earnings per share	$ (0.34)	$ (0.44)	$ (0.52)	$ (0.58)	$ (0.53)	$ (0.67)	$ (0.62)	$ (0.65)	$ (1.86)	$ (2.46)	$ (2.47)
Diluted earnings per share	$ (0.34)	$ (0.44)	$ (0.52)	$ (0.58)	$ (0.53)	$ (0.67)	$ (0.62)	$ (0.65)	$ (1.86)	$ (2.46)	$ (2.47)
Antidilutive potential common shares excluded from computation of earnings per share									2,100	2,000	1,769
Notes due 2019 [Member]
Denominator
Debt Instrument, Convertible, Stock Price Trigger									$ 33.79
Notes due 2047 [Member]
Denominator
Debt Instrument, Convertible, Stock Price Trigger									$ 48.63

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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