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Dividends (Details) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dividends (Textual)      
Initial dividend rate 6.50% 6.50%  
Increase in dividend rate on default of payment 7.50% 10.00%  
Increase in dividend rate on two consecutive default of payment 10.00% 7.50%  
Series A convertible preferred stock outstanding (in shares) 13,602 13,602 13,602
Amount of arrears dividend $ 196,000 $ 187,000  
Series A convertible preferred stock liquidation preference (in dollars per share) $ 25.00 $ 25.00  
Percentage of weighted average of common stock sales price 95.00% 95.00%  
Percentage of increase in dividend rate   1.00%  
Convertible Preferred Stock [Member]      
Dividends (Textual)      
Initial dividend rate 6.50%