| Summary of Significant Accounting Policies - Leases - General Information (Details) - USD ($) $ in Thousands | Jan. 01, 2019 | Sep. 30, 2019 | Dec. 31, 2017 | 
|---|---|---|---|
| Cumulative effect of applying new accounting standards | $ 0 | $ 8,645 | |
| Operating lease right-of-use assets | $ 20,563 | ||
| Operating lease liability | $ 24,935 | ||
| ASU 2016-02 | Restatement Adjustment | |||
| Operating lease right-of-use assets | 22,200 | ||
| Operating lease liability | 26,900 | ||
| Decrease in other liabilities and prepayments | $ 4,700 | 
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- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. No definition available. 
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- Definition The increase (decrease) during the reporting period in other expenses incurred but not yet paid. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Present value of lessee's discounted obligation for lease payments from operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- Definition Amount of lessee's right to use underlying asset under operating lease. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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