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Interest Expense (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2017
Interest and Debt Expense [Abstract] |  |  |  |  |  |
Interest incurred on debt | $ 31,389 | $ 22,554 | $ 63,509 | $ 35,473 |  |
Related-party Promissory Note interest expense | 0 | 5,090 | 0 | 5,090 |  |
Senior Note redemption premium | 0 | 0 | 0 | 4,782 |  |
Accretion of fair value adjustment on Senior Notes | 0 | 0 | 0 | 19,414 |  |
Accretion of original issue discount on 2018 Term Loans | 549 | 268 | 1,098 | 357 |  |
Amortization of debt issuance costs | 1,031 | 755 | 2,062 | 1,416 |  |
Total interest expense | $ 32,969 | $ 28,667 | $ 66,669 | 66,532 |  |
Effective interest rate, revolving credit facility |  |  | 5.90% |  | 4.57% |
Stated interest rate |  |  |  |  |  | 6.375%
Accelerated Accretion |  |  |  | 18,700 |  |
Accelerated Amortization of Debt Issuance Costs |  |  |  | $ 300 |  |

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