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Equity-Method Investments - Narrative (Details) - NMTC Program - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Oct. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]      
Membership interest 99.90%    
Equity contributions $ 4.1 $ 22.8 $ 22.9
Total contributions to be paid over obligation term $ 49.8    
Obligation term 2 years