Change in Accounting Principle (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) item	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Aug. 31, 2016 USD ($)
Change in Accounting Principle
Warrant liability				$ 1,500,000		$ 1,900,000
Warrant derivative loss (gain)				400,000		(17,100,000)
Accumulated Deficit	$ (510,019,000)	$ (509,082,000)	$ (510,019,000)		$ (509,082,000)
Number of open contracts | item			1
Gain on sale of assets			$ 4,335,000	605,000
Trading securities		238,000			238,000
Available for sale equity unrealized losses					40,000
Retained earnings and other comprehensive income adjustment			(40,000)
Trading securities loss	16,000
Trading securities gain			51,000
ASU 2017-11 Earnings Per Share
Change in Accounting Principle
Warrant derivative loss (gain)			8,000	$ 3,000		$ 300,000
Sale, not discontinued operations | Zacatecas
Change in Accounting Principle
Total consideration	$ 1,500,000		1,500,000				$ 1,500,000
Gain on sale of assets			523,000
Sale, not discontinued operations | Zacatecas | ASU 2014-09 Revenue from Contracts with Customers
Change in Accounting Principle
Gain on sale of assets			$ 49,000
Sale, not discontinued operations | Zacatecas | Previously Reported
Change in Accounting Principle
Gain on sale of assets		49,000
Sale, not discontinued operations | Zacatecas | Cumulative Effect Adjustment | ASU 2014-09 Revenue from Contracts with Customers
Change in Accounting Principle
Accumulated Deficit		$ (49,000)			$ (49,000)