Fair Value Measurements (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) Investment	Dec. 31, 2015 USD ($)
Financial Liabilities [Abstract]
Number of bond investments | Investment	3
Investments included in Level 2 were transferred to Level 1	$ 610
Net unrealized gains or losses incurred	(154)	$ (429)
Measured at Fair Value on a Recurring Basis [Member]
Financial Assets [Abstract]
Derivative financial instruments	306	1,265
Total financial assets	14,856	14,344
Financial Liabilities [Abstract]
SERP liabilities	7,171	5,869
Derivative financial instruments	397	22
Total financial liabilities	7,568	5,891
Measured at Fair Value on a Recurring Basis [Member] | SERP Money Market Fund [Member]
Financial Assets [Abstract]
Investments	461	445
Measured at Fair Value on a Recurring Basis [Member] | SERP Mutual Funds [Member]
Financial Assets [Abstract]
Investments	3,055	2,864
Measured at Fair Value on a Recurring Basis [Member] | Preferred Stocks [Member]
Financial Assets [Abstract]
Investments	505	742
Measured at Fair Value on a Recurring Basis [Member] | Corporate Bonds [Member]
Financial Assets [Abstract]
Investments	4,251	3,897
Measured at Fair Value on a Recurring Basis [Member] | Municipal Bonds [Member]
Financial Assets [Abstract]
Investments	3,029	1,811
Measured at Fair Value on a Recurring Basis [Member] | Floating Rate Notes [Member]
Financial Assets [Abstract]
Investments	87	84
Measured at Fair Value on a Recurring Basis [Member] | U.S. Treasury Bills [Member]
Financial Assets [Abstract]
Investments		404
Measured at Fair Value on a Recurring Basis [Member] | Asset Backed Securities [Member]
Financial Assets [Abstract]
Investments	739
Measured at Fair Value on a Recurring Basis [Member] | Saving Bonds [Member]
Financial Assets [Abstract]
Investments	47	77
Measured at Fair Value on a Recurring Basis [Member] | Other [Member]
Financial Assets [Abstract]
Investments	2,376	2,755
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member]
Financial Assets [Abstract]
Derivative financial instruments	0	0
Total financial assets	8,406	8,372
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	461	445
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | SERP Mutual Funds [Member]
Financial Assets [Abstract]
Investments	3,055	2,864
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Preferred Stocks [Member]
Financial Assets [Abstract]
Investments	505	742
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Corporate Bonds [Member]
Financial Assets [Abstract]
Investments	4,251	3,756
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	87	84
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | U.S. Treasury Bills [Member]
Financial Assets [Abstract]
Investments		404
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Asset Backed Securities [Member]
Financial Assets [Abstract]
Investments	0
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Saving Bonds [Member]
Financial Assets [Abstract]
Investments	47	77
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	306	1,265
Total financial assets	6,450	5,972
Financial Liabilities [Abstract]
SERP liabilities	7,171	5,869
Derivative financial instruments	397	22
Total financial liabilities	7,568	5,891
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	141
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Municipal Bonds [Member]
Financial Assets [Abstract]
Investments	3,029	1,811
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	739
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Saving Bonds [Member]
Financial Assets [Abstract]
Investments	0	0
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Other [Member]
Financial Assets [Abstract]
Investments	$ 2,376	$ 2,755