Summary of Significant Accounting Policies - Retirement Benefits (Details) - USD ($) |
12 Months Ended | ||
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Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
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| Summary of Significant Accounting Policies | |||
| Pension contributions | $ 1,847,000 | $ 1,264,000 | $ 976,000 |
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- References No definition available.
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- Definition Amount of cost for defined contribution plan. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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