Long-Term Debt and Notes Payable (Tables)  | 
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Dec. 31, 2017  | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Debt Disclosure [Abstract] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Summary of Long-Term Debt | 
 Long-term debt consists of the following: 
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| Principal Maturities of Long-Term Debt | 
 Principal maturities of long-term debt are approximately: 
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- References No definition available. 
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- Definition Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation. No definition available. 
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- Definition Tabular disclosure of the combined aggregate amount of maturities and sinking fund requirements for all long-term borrowings for each of the five years following the date of the latest balance sheet date presented. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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