Fair Value Measurements (Details) - USD ($) $ in Thousands | 6 Months Ended | 12 Months Ended |
Jun. 30, 2017 | Dec. 31, 2016 |
Financial Liabilities [Abstract] | | |
Net unrealized gains (losses) incurred | $ 123 | $ (107) |
Measured at Fair Value on a Recurring Basis [Member] | | |
Financial Assets [Abstract] | | |
Derivative financial instruments | | 144 |
Total financial assets | 16,059 | 15,133 |
Financial Liabilities [Abstract] | | |
SERP liabilities | 7,814 | 7,882 |
Derivative financial instruments | 161 | 89 |
Total financial liabilities | 7,975 | 7,971 |
Measured at Fair Value on a Recurring Basis [Member] | SERP Money Market Fund [Member] | | |
Financial Assets [Abstract] | | |
Investments | 385 | 92 |
Measured at Fair Value on a Recurring Basis [Member] | SERP Mutual Funds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 3,892 | 3,335 |
Measured at Fair Value on a Recurring Basis [Member] | Preferred Stocks [Member] | | |
Financial Assets [Abstract] | | |
Investments | 364 | 475 |
Measured at Fair Value on a Recurring Basis [Member] | Corporate Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 5,673 | 5,413 |
Measured at Fair Value on a Recurring Basis [Member] | Municipal Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 2,512 | 2,248 |
Measured at Fair Value on a Recurring Basis [Member] | Floating Rate Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 401 | 118 |
Measured at Fair Value on a Recurring Basis [Member] | U.S. Treasury Bills [Member] | | |
Financial Assets [Abstract] | | |
Investments | | 388 |
Measured at Fair Value on a Recurring Basis [Member] | Asset Backed Securities [Member] | | |
Financial Assets [Abstract] | | |
Investments | 588 | 637 |
Measured at Fair Value on a Recurring Basis [Member] | U.S. Treasury Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 541 | |
Measured at Fair Value on a Recurring Basis [Member] | Other [Member] | | |
Financial Assets [Abstract] | | |
Investments | 1,703 | 2,283 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | | |
Financial Assets [Abstract] | | |
Derivative financial instruments | | 0 |
Total financial assets | 11,256 | 9,821 |
Financial Liabilities [Abstract] | | |
SERP liabilities | 0 | 0 |
Derivative financial instruments | 0 | 0 |
Total financial liabilities | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | SERP Money Market Fund [Member] | | |
Financial Assets [Abstract] | | |
Investments | 385 | 92 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | SERP Mutual Funds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 3,892 | 3,335 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Preferred Stocks [Member] | | |
Financial Assets [Abstract] | | |
Investments | 364 | 475 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Corporate Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 5,673 | 5,413 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Municipal Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Floating Rate Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 401 | 118 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | U.S. Treasury Bills [Member] | | |
Financial Assets [Abstract] | | |
Investments | | 388 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Asset Backed Securities [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | U.S. Treasury Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 541 | |
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Other [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | | |
Financial Assets [Abstract] | | |
Derivative financial instruments | | 144 |
Total financial assets | 4,803 | 5,312 |
Financial Liabilities [Abstract] | | |
SERP liabilities | 7,814 | 7,882 |
Derivative financial instruments | 161 | 89 |
Total financial liabilities | 7,975 | 7,971 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | SERP Money Market Fund [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | SERP Mutual Funds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Preferred Stocks [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Corporate Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Municipal Bonds [Member] | | |
Financial Assets [Abstract] | | |
Investments | 2,512 | 2,248 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Floating Rate Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | U.S. Treasury Bills [Member] | | |
Financial Assets [Abstract] | | |
Investments | | 0 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Asset Backed Securities [Member] | | |
Financial Assets [Abstract] | | |
Investments | 588 | 637 |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | U.S. Treasury Notes [Member] | | |
Financial Assets [Abstract] | | |
Investments | 0 | |
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Other [Member] | | |
Financial Assets [Abstract] | | |
Investments | $ 1,703 | $ 2,283 |