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Long-term Debt Senior Convertible Notes (Details) - USD ($) |  | 12 Months Ended
--- | --- | ---
Aug. 12, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Senior Convertible Notes [Line Items] |  |  |  |
Senior Convertible Notes, net carrying amount |  | $ 139,107,000 | $ 130,856,000 |
Capped call transaction costs |  |  | 24,195,000 |
Capped call, cap price |  | $ 60.00 |  |
Capitalized interest costs |  | $ 12,600,000 | 17,000,000 | $ 25,100,000
1.50% Senior Convertible Notes Due 2021 [Member] |  |  |  |
Senior Convertible Notes [Line Items] |  |  |  |
Senior Convertible Notes, face amount |  | $ 172,500,000 | 172,500,000 |
Senior Convertible Notes, interest rate, stated percentage |  | 1.50% |  |
Net proceeds from Senior Convertible Notes |  |  | 166,600,000 |
Senior Convertible Notes debt issuance costs, gross |  |  | 5,900,000 |
Senior Convertible Notes, threshold trading days |  | 20 |  |
Senior Convertible Notes, threshold consecutive trading days |  | 30 |  |
Senior Convertible Notes, threshold percentage of stock price trigger |  | 130.00% |  |
Senior Convertible Notes, threshold business days, trading price trigger |  | 5 days |  |
Senior Convertible Notes, threshold trading days, trading price trigger |  | 5 days |  |
Senior Convertible Notes, principal amount of note |  | $ 1,000 |  |
Senior Convertible Notes, threshold percentage of trading price trigger |  | 98.00% |  |
Senior Convertible Notes, conversion rate |  | 24.6914 |  |
Senior Convertible Notes, conversion price |  | $ 40.50 |  |
Senior Convertible Notes, initial fair value of liability component | $ 132,300,000 |  |  |
Senior Convertible Notes, effective interest rate | 7.25% |  |  |
Senior Convertible Notes, initial value of equity component | $ 40,217,000 | $ 40,217,000 | 40,217,000 |
Senior Convertible Notes, interest expense |  | 9,900,000 | 3,700,000 |
Senior Convertible Notes, unamortized discount |  | (30,183,000) | (37,513,000) |
Unamortized deferred financing costs |  | 3,210,000 | 4,131,000 |
Senior Convertible Notes, net carrying amount |  | 139,107,000 | 130,856,000 |
Senior Convertible Notes, related issuance costs, equity component |  | (1,375,000) | (1,375,000) |
Senior Convertible Notes, deferred tax liability, equity component |  | 5,267,000 | 5,267,000 |
Senior Convertible Notes, net carrying amount, equity component |  | $ 33,575,000 | $ 33,575,000 |

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