Change in Accounting Principle (Details) - USD ($)	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in Accounting Principle
Warrant liability			$ 1,500,000
Warrant derivative loss (gain)			400,000
Accumulated Deficit		$ (509,082,000)		$ (511,124,000)	$ (509,082,000)
Gain on sale of assets				5,144,000	608,000
Trading securities		238,000		275,000	238,000
Available for sale equity unrealized losses					$ 40,000
Retained earnings and other comprehensive income adjustment				40,000
Trading securities gain				51,000
ASU 2017-11 Earnings Per Share
Change in Accounting Principle
Warrant derivative loss (gain)			$ 3,000	8,000		$ 300,000
Sale, not discontinued operations | Zacatecas
Change in Accounting Principle
Total consideration				1,500,000
Gain on sale of assets				748,000
Sale, not discontinued operations | Zacatecas | ASU 2014-09 Revenue from Contracts with Customers
Change in Accounting Principle
Gain on sale of assets	$ 49,000	$ 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