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Interest and Debt Expense - Footnote (Details) - Senior Unsecured Notes - Senior Unsecured Notes Due 2022
6 Months Ended
Jun. 30, 2019
USD ($)
Debt Instrument, Redemption [Line Items]  
Debt prepayment costs $ 22,540,000
Debt instrument, redeemed $ 400,000,000
Debt instrument, interest rate, stated percentage (percent) 5.00%