Debt - Redemption Prices (Details) - Senior Notes - 7.875% senior notes due 2021	12 Months Ended
	Dec. 31, 2017
On or after August 1, 2017, but before August 1, 2018
Debt Instrument [Line Items]
Redemption price, as a percent of the of principal amount	103.90%
On or after August 1, 2018, but before August 1, 2019
Debt Instrument [Line Items]
Redemption price, as a percent of the of principal amount	102.00%
On or after August 1, 2019 and thereafter
Debt Instrument [Line Items]
Redemption price, as a percent of the of principal amount	100.00%