Debt - Senior Notes (Details) - Senior Notes	Mar. 31, 2018
6.00% Senior Notes, due 2026
Debt Instrument [Line Items]
Interest rate	6.00%
5.875% Senior Notes, due 2024
Debt Instrument [Line Items]
Interest rate	5.875%
5.125% Senior Notes, due 2023
Debt Instrument [Line Items]
Interest rate	5.125%
5.875% Senior Notes due 2022
Debt Instrument [Line Items]
Interest rate	5.875%