| **Leases - Additional information (Details) - USD ($) $ in Thousands** | Mar. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018 |
|------------------------------------------------------------------------|---------------|---------------|---------------|
| **Operating Leased Assets [Line Items]**                               |          |          |          |
| Operating lease right-of-use assets (Note 16)                          | $ 193,897     | $ 194,000     | $ 0           |
| Operating lease, liability                                             | 119,139       | 119,000       |          |
| Other                                                                  | (39,257)      |          | (129,312)     |
| Other current liabilities                                              | $ (114,361)   |          | $ (184,229)   |
| Accounting Standards Update 2016-02                                    |          |          |          |
| **Operating Leased Assets [Line Items]**                               |          |          |          |
| Other                                                                  |          | 85,000        |          |
| Other current liabilities                                              |          | $ 10,000      |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Present value of lessee's discounted obligation for lease payments from operating lease.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of lessee's right to use underlying asset under operating lease.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net amount of other deferred costs capitalized at the end of the reporting period. Does not include deferred finance costs or deferred acquisition costs of insurance companies.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer.
+ References
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| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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