Fair Value Measurements (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) Investment	Dec. 31, 2015 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments included in Level 1 were transferred to Level 2	$ 636
Financial Liabilities [Abstract]
Net unrealized losses incurred	$ (238)	$ (429)
Number of bond investments | Investment	3
Measured at Fair Value on a Recurring Basis [Member]
Financial Assets [Abstract]
Derivative financial instruments	$ 488	1,265
Total financial assets	14,385	14,344
Financial Liabilities [Abstract]
SERP liabilities	6,307	5,869
Derivative financial instruments	526
Total financial liabilities	6,833	5,869
Measured at Fair Value on a Recurring Basis [Member] | SERP Money Market Fund [Member]
Financial Assets [Abstract]
Investments	453	445
Measured at Fair Value on a Recurring Basis [Member] | SERP Mutual Funds [Member]
Financial Assets [Abstract]
Investments	2,895	2,864
Measured at Fair Value on a Recurring Basis [Member] | Preferred Stocks [Member]
Financial Assets [Abstract]
Investments	1,008	742
Measured at Fair Value on a Recurring Basis [Member] | Corporate Bonds [Member]
Financial Assets [Abstract]
Investments	3,442	3,897
Measured at Fair Value on a Recurring Basis [Member] | Municipal Bonds [Member]
Financial Assets [Abstract]
Investments	3,036	1,811
Measured at Fair Value on a Recurring Basis [Member] | Floating Rate Notes [Member]
Financial Assets [Abstract]
Investments	72	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	779
Measured at Fair Value on a Recurring Basis [Member] | Saving Bonds [Member]
Financial Assets [Abstract]
Investments	84	77
Measured at Fair Value on a Recurring Basis [Member] | Other [Member]
Financial Assets [Abstract]
Investments	2,128	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	7,333	8,372
Financial Liabilities [Abstract]
SERP liabilities	0	0
Derivative financial instruments	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	453	445
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | SERP Mutual Funds [Member]
Financial Assets [Abstract]
Investments	2,895	2,864
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Preferred Stocks [Member]
Financial Assets [Abstract]
Investments	1,008	742
Measured at Fair Value on a Recurring Basis [Member] | Level 1 [Member] | Corporate Bonds [Member]
Financial Assets [Abstract]
Investments	2,821	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	72	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	84	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	488	1,265
Total financial assets	7,052	5,972
Financial Liabilities [Abstract]
SERP liabilities	6,307	5,869
Derivative financial instruments	526
Total financial liabilities	6,833	5,869
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	621	141
Measured at Fair Value on a Recurring Basis [Member] | Level 2 [Member] | Municipal Bonds [Member]
Financial Assets [Abstract]
Investments	3,036	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	779
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	$ 2,128	$ 2,755