Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
Dec. 31, 2017 |
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| Accounting Policies [Abstract] | |||||
| Realized gains (losses) recognized on available-for-sale investments | $ 0.8 | $ 0.0 | $ 0.7 | $ 0.0 | |
| Reduction in deferred tax asset value and valuation allowance | $ 3.7 | ||||
| X | ||||||||||
- Definition Debt Securities, Available-For-Sale, Realized Gain (Loss) No definition available.
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| X | ||||||||||
- Definition Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Change in Tax Rate, Income Tax Expense (Benefit), Before Valuation Allowance Impact No definition available.
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| X | ||||||||||
- References No definition available.
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