Condensed Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, plant, and equipment, accumulated depreciation	$ 15,882	$ 14,403
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	246,975,173	234,160,661
Common stock in treasury, shares	15,020,437	15,002,663
Series C Redeemable Convertible Preferred Stock
Redeemable convertible Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Redeemable convertible Preferred Stock, shares authorized	10,431	10,431
Redeemable convertible Preferred Stock, shares issued	2,620	2,620
Redeemable convertible Preferred Stock, shares outstanding	2,620	2,620
Redeemable convertible Preferred Stock, aggregate involuntary liquidation preference (in dollars)	$ 16,664	$ 16,664
Series E Redeemable Convertible Preferred Stock
Redeemable convertible Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Redeemable convertible Preferred Stock, shares authorized	35,000	35,000
Redeemable convertible Preferred Stock, shares issued	35,000	35,000
Redeemable convertible Preferred Stock, shares outstanding	35,000	35,000
Redeemable convertible Preferred Stock, aggregate involuntary liquidation preference (in dollars)	$ 35,000	$ 35,000

Cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land or leased assets).

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