| Stock Award Plans (Details) | 3 Months Ended | 
|---|---|
| Mar. 31, 2017  plan | |
| Stock Based Compensation | |
| Number of stock option plans | 4 | 
| 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 | ||||||||||
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- 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 | ||||||||||
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- Definition Represents the number of stock option plans under the share-based compensation arrangements. No definition available. 
 | 
| X | ||||||||||
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- References No definition available. 
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| X | ||||||||||
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- Definition Purchase price of common stock expressed as a percentage of its fair value. No definition available. 
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| X | ||||||||||
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- Details 
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