Long-Term Debt Long-term debt - Early redemption premium percentages (Details) - Senior Notes [Member] - Senior Unsecured Notes due 2025 [Member]	6 Months Ended
	Jun. 30, 2017
Debt Instrument, Redemption, Period One [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	103.188%
Debt Instrument, Redemption, Period Two [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	101.594%
Debt Instrument, Redemption, Period Three [Member]
Debt Instrument [Line Items]
Debt Instrument, Redemption Price, Percentage	100.00%