Fair Value Measurements - Summary of Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Financial liabilities:
Capital leases	$ 484	$ 917
7% Senior Notes due 2023
Financial liabilities:
Long-term debt	368,630	367,854
6% Senior Notes due 2025
Financial liabilities:
Long-term debt	880,289	880,889
6% Senior Notes due 2026
Financial liabilities:
Long-term debt	598,105
Term Loan
Financial liabilities:
Long-term debt	937,910	938,002
Carrying Amount
Financial liabilities:
Capital leases	484	917
Carrying Amount | 7% Senior Notes due 2023
Financial liabilities:
Long-term debt	368,630	367,854
Carrying Amount | 6% Senior Notes due 2025
Financial liabilities:
Long-term debt	880,289	880,889
Carrying Amount | 6% Senior Notes due 2026
Financial liabilities:
Long-term debt	598,105	0
Carrying Amount | Term Loan
Financial liabilities:
Long-term debt	937,910	938,002
Carrying Amount | Revolving Credit Facility
Financial liabilities:
Long-term debt	180,000	0
Carrying Amount | Other long-term debt
Financial liabilities:
Long-term debt	2,463	2,531
Fair Value
Financial liabilities:
Capital leases	484	917
Fair Value | 7% Senior Notes due 2023
Financial liabilities:
Long-term debt	393,750	400,800
Fair Value | 6% Senior Notes due 2025
Financial liabilities:
Long-term debt	889,263	914,375
Fair Value | 6% Senior Notes due 2026
Financial liabilities:
Long-term debt	606,000	0
Fair Value | Term Loan
Financial liabilities:
Long-term debt	961,534	956,750
Fair Value | Revolving Credit Facility
Financial liabilities:
Long-term debt	180,000	0
Fair Value | Other long-term debt
Financial liabilities:
Long-term debt	$ 2,463	$ 2,531