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Long-term Debt Senior Notes (Details) - USD ($) $ in Thousands |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Aug. 20, 2018 | Jul. 16, 2018 | Jun. 15, 2018 | Sep. 12, 2016 | May 21, 2015 | Nov. 17, 2014 | May 20, 2013 | Sep. 30, 2018 | Mar. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 2,448,439 | $ 2,769,663 |
Gain (loss) on extinguishment of debt |  |  |  |  |  |  |  |  |  | (26,740) | (35) | $ 15,722
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 6,334 | 22 | (15,722)
6.50% Senior Notes Due 2021 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 6.50% |  |
Principal amount |  |  |  |  |  |  |  |  |  | $ 0 | 344,611 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | 0 | (2,656) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | 0 | 341,955 |
Senior Notes, repurchased face amount |  |  | $ 344,611 |  |  |  |  |  |  |  |  |
Premiums paid for extinguishment of debt |  |  |  |  |  |  |  |  |  | 7,500 |  |
Senior Notes repurchased, settlement amount |  | $ 355,900 |  |  |  |  |  |  |  |  |  |
Gain (loss) on extinguishment of debt |  |  |  |  |  |  |  |  |  | 9,800 |  |
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 2,300 |  |
Senior Notes, redemption price, percentage |  |  | 102.167% |  |  |  |  |  |  |  |  |
6.125% Senior Notes Due 2022 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 6.125% |  |
Principal amount |  |  |  |  |  | $ 600,000 |  |  |  | $ 476,796 | 561,796 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (3,921) | (5,800) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 472,875 | 555,996 |
Senior Notes, repurchased face amount |  |  |  |  |  |  |  | $ 85,000 | $ 38,200 |  |  |
Senior Notes repurchased, settlement amount |  |  |  |  |  |  |  | 89,500 | 24,300 |  |  |
Net proceeds from Senior Notes issuance |  |  |  |  |  | 590,000 |  |  |  |  |  |
Senior Notes debt issuance costs |  |  |  |  |  | $ 10,000 |  |  |  |  |  |
6.50% Senior Notes Due 2023 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 6.50% |  |
Principal amount |  |  |  |  |  |  |  |  |  | $ 0 | 394,985 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | 0 | (3,707) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 0 | 391,278 |
Senior Notes, repurchased face amount |  |  |  |  |  |  |  | 394,985 | 5,000 |  |  |
Senior Notes repurchased, settlement amount |  |  |  |  |  |  |  | 408,300 | 3,300 |  |  |
5% Senior Notes Due 2024 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 5.00% |  |
Principal amount |  |  |  |  |  |  | $ 500,000 |  |  | $ 500,000 | 500,000 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (4,688) | (5,610) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 495,312 | 494,390 |
Net proceeds from Senior Notes issuance |  |  |  |  |  |  | 490,200 |  |  |  |  |
Senior Notes debt issuance costs |  |  |  |  |  |  | $ 9,800 |  |  |  |  |
5.625% Senior Notes Due 2025 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 5.625% |  |
Principal amount |  |  |  |  | $ 500,000 |  |  |  |  | $ 500,000 | 500,000 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (5,808) | (6,714) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 494,192 | 493,286 |
Net proceeds from Senior Notes issuance |  |  |  |  | 491,000 |  |  |  |  |  |  |
Senior Notes debt issuance costs |  |  |  |  | $ 9,000 |  |  |  |  |  |  |
6.75% Senior Notes Due 2026 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 6.75% |  |
Principal amount |  |  |  | $ 500,000 |  |  |  |  |  | $ 500,000 | 500,000 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (6,407) | (7,242) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 493,593 | 492,758 |
Net proceeds from Senior Notes issuance |  |  |  | 491,600 |  |  |  |  |  |  |  |
Senior Notes debt issuance costs |  |  |  | $ 8,400 |  |  |  |  |  |  |  |
6.625% Senior Notes Due 2027 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes, interest rate, stated percentage |  |  |  |  |  |  |  |  |  | 6.625% |  |
Principal amount | $ 500,000 |  |  |  |  |  |  |  |  | $ 500,000 | 0 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (7,533) | 0 |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | 492,467 | 0 |
Net proceeds from Senior Notes issuance | 492,100 |  |  |  |  |  |  |  |  |  |  |
Senior Notes debt issuance costs | $ 7,900 |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Principal amount |  |  |  |  |  |  |  |  |  | 2,476,796 | 2,801,392 |
Unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | (28,357) | (31,729) |
Principal amount, net of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | 2,448,439 | $ 2,769,663 |
Senior Notes, repurchased face amount |  |  |  |  |  |  |  |  | 46,300 |  |  |
Senior Notes repurchased, settlement amount |  |  |  |  |  |  |  |  | $ 29,900 |  |  |
Gain (loss) on extinguishment of debt |  |  |  |  |  |  |  |  |  |  |  | 15,700
Senior Notes repurchased, discount |  |  |  |  |  |  |  |  |  |  |  | 16,400
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  |  |  | $ 700
6.125% Senior Notes Due 2022 and 6.50% Senior Notes Due 2023 [Member] |  |  |  |  |  |  |  |  |  |  |  |
Senior Notes [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Premiums paid for extinguishment of debt |  |  |  |  |  |  |  |  |  | 12,900 |  |
Senior Notes repurchased, settlement amount |  |  |  |  |  |  |  | $ 497,800 |  |  |  |
Gain (loss) on extinguishment of debt |  |  |  |  |  |  |  |  |  | 16,900 |  |
Loss on extinguishment of debt, acceleration of unamortized deferred financing costs |  |  |  |  |  |  |  |  |  | $ 4,000 |  |

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