Stock Award Plans (Details)  | 
6 Months Ended | 
|---|---|
| 
 Jun. 30, 2018  
plan 
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| Stock Based Compensation | |
| Number of stock option plans | 2 | 
| Purchase Plan | |
| Stock Based Compensation | |
| Purchase price of common shares as a percentage of the fair market value on the first day of the offering period | 85.00% | 
| Purchase price of common shares as a percentage of the fair market value on the purchase date | 85.00% | 
| X | ||||||||||
- Definition Represents the purchase price expressed as a percentage of the fair market value of common stock on the first day of the offering period. No definition available. 
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| X | ||||||||||
- Definition Represents the number of stock option plans under the share-based compensation arrangements. No definition available. 
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| X | ||||||||||
- References No definition available. 
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| X | ||||||||||
- Definition Purchase price of common stock expressed as a percentage of its fair value. No definition available. 
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| X | ||||||||||
- Details 
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