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Derivative Financial Instruments and Hedging Activities - Narrative (Details)
12 Months Ended
Dec. 31, 2017
contract
Jun. 30, 2019
USD ($)
Derivative [Line Items]    
Debt instrument, face amount   $ 270,000,000.0
Cash collateral held by a counterparty to a master netting agreement   $ 7,400,000
Interest Rate Swap    
Derivative [Line Items]    
Derivative, instruments terminated | contract 2