Consolidated Statements of Cash Flows (Parenthetical)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
5 7/8% Senior Notes due January 31, 2025
Debt instrument interest rate	5.875%	5.875%	5.875%
7% Senior Notes due 2022
Debt instrument interest rate	7.00%	7.00%	7.00%
8 1/2% Senior Notes due 2020
Debt instrument interest rate	8.50%	8.50%	8.50%