Fair Value Measurements - Carrying Values and Estimated Fair Values of Financial Instruments (Details) - Level 2 - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total debt	$ 2,195,000	$ 3,759,000
Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total debt	2,213,790	3,984,699
Term Loan, Secured Due April 2024 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Term loan	975,000
Term Loan, Secured Due April 2024 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Term loan	975,000
6.875% Notes, Unsecured, Due April 2022, Issued 2017 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable	700,000
6.875% Notes, Unsecured, Due April 2022, Issued 2017 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable	713,790
7.125% Notes, Unsecured, Due April 2025, Issued 2017 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable	500,000
7.125% Notes, Unsecured, Due April 2025, Issued 2017 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable	505,000
Credit Facility Secured Due January 2022 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Credit facility	20,000
Credit Facility Secured Due January 2022 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Credit facility	$ 20,000
7.31% Notes Due March 2016, Issued 2009 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		62,000
7.31% Notes Due March 2016, Issued 2009 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		64,266
4.98% Notes Due January 2017, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		116,000
4.98% Notes Due January 2017, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		123,967
5.92% Notes Due March 2018, Issued 2008 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		200,000
5.92% Notes Due March 2018, Issued 2008 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		224,025
5.75% Notes Due December 2018, Issued 2013 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		450,000
5.75% Notes Due December 2018, Issued 2013 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		465,630
7.77% Notes Due March 2019, Issued 2009 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		173,000
7.77% Notes Due March 2019, Issued 2009 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		204,854
5.50% Notes Due January 2020, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		207,000
5.50% Notes Due January 2020, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		233,932
4.51% Notes Due October 2020, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		315,000
4.51% Notes Due October 2020, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		337,528
5.60% Notes Due January 2022, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		87,000
5.60% Notes Due January 2022, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		99,983
4.66% Notes Due October 2022, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		35,000
4.66% Notes Due October 2022, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		38,225
6.125% Notes Due October 2024, Issued 2014 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		850,000
6.125% Notes Due October 2024, Issued 2014 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		893,325
5.85% Notes Due January 2025, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		90,000
5.85% Notes Due January 2025, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		106,299
4.91% Notes Due October 2025, Issued 2010 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		175,000
4.91% Notes Due October 2025, Issued 2010 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Notes payable		193,665
Credit Facility Due October 2016 | Carrying Amount
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Credit facility		999,000
Credit Facility Due October 2016 | Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Credit facility		$ 999,000