Summary of Significant Accounting Policies (Details) - USD ($) |
3 Months Ended | 12 Months Ended | |
|---|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
Dec. 31, 2017 |
|
| Accounting Policies [Abstract] | |||
| Realized losses recognized on available-for-sale investments | $ 200,000 | ||
| Realized gains (losses) recognized on available-for-sale investments | $ 0 | ||
| Effect of remeasurement of deferred tax assets and liabilities under Tax Cuts and Jobs Act | $ 3,700,000 | ||
| 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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| X | ||||||||||
- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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