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Debt and Credit Arrangements - Letters of Credit (Details) - USD ($)
$ in Millions
Jun. 30, 2019
Dec. 31, 2018
Jun. 30, 2018
Debt Disclosure [Abstract]      
Restricted cash $ 1.0 $ 1.0  
Restricted cash, noncurrent $ 1.0 $ 1.0 $ 1.0