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Debt and Credit Arrangements - 2018 Notes (Details) - Convertible Notes, Due 2018 - Convertible Debt - USD ($)
9 Months Ended
Sep. 30, 2018
Jun. 30, 2019
Aug. 01, 2018
Debt Instrument      
Debt instrument stated interest rate (percent)     2.00%
Debt instrument face amount     $ 57,100,000
Repayment of debt $ 57,100,000    
Interest paid $ 600,000    
Percentage of expired warrants (percent)   90.00%