Fair Value Measurements - Carrying Values and Estimated Fair Values of Financial Instruments (Parenthetical) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Term Loan, Secured Due April 2024
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year	2024-04
6.875% Notes, Unsecured, Due April 2022, Issued 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year	2022-04
Stated interest rate	6.875%
Debt instrument issuance year	2017
7.125% Notes, Unsecured, Due April 2025, Issued 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year	2025-04
Stated interest rate	7.125%
Debt instrument issuance year	2017
Credit Facility Secured Due January 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year	2022-01
7.31% Notes Due March 2016, Issued 2009
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2016-03
Stated interest rate		7.31%
Debt instrument issuance year		2009
4.98% Notes Due January 2017, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2017-01
Stated interest rate		4.98%
Debt instrument issuance year		2010
5.92% Notes Due March 2018, Issued 2008
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2018-03
Stated interest rate		5.92%
Debt instrument issuance year		2008
5.75% Notes Due December 2018, Issued 2013
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2018-12
Stated interest rate		5.75%
Debt instrument issuance year		2013
7.77% Notes Due March 2019, Issued 2009
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2019-03
Stated interest rate		7.77%
Debt instrument issuance year		2009
5.50% Notes Due January 2020, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2020-01
Stated interest rate		5.50%
Debt instrument issuance year		2010
4.51% Notes Due October 2020, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2020-10
Stated interest rate		4.51%
Debt instrument issuance year		2010
5.60% Notes Due January 2022, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2022-01
Stated interest rate		5.60%
Debt instrument issuance year		2010
4.66% Notes Due October 2022, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2022-10
Stated interest rate		4.66%
Debt instrument issuance year		2010
6.125% Notes Due October 2024, Issued 2014
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2024-10
Stated interest rate		6.125%
Debt instrument issuance year		2014
5.85% Notes Due January 2025, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2025-01
Stated interest rate		5.85%
Debt instrument issuance year		2010
4.91% Notes Due October 2025, Issued 2010
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2025-10
Stated interest rate		4.91%
Debt instrument issuance year		2010
Credit Facility Due October 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instruments maturity month and year		2016-10