Financial Instruments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation trust assets	$ 42,161	$ 46,145
Fair value of interest rate derivatives	(194)	191
Deferred compensation plan, asset	42,296	46,215
Deferred compensation liability	33,287	37,280
Deferred compensation plan, liability	33,357	37,772
Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation trust assets	0	0
Deferred compensation plan, asset	0	0
Deferred compensation liability	0	0
Deferred compensation plan, liability	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation trust assets	42,161	46,145
Deferred compensation plan, asset	42,296	46,215
Deferred compensation liability	33,287	37,280
Deferred compensation plan, liability	33,357	37,772
Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation trust assets	0	0
Deferred compensation plan, asset	0	0
Deferred compensation liability	0	0
Deferred compensation plan, liability	$ 0	0
Interest Rate Swap No. 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative, term of contract	5 years
Fair value of interest rate derivatives	$ 135	70
Interest Rate Swap No. 2 [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives	$ 0	0
Interest Rate Swap No. 2 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative, term of contract	5 years
Fair value of interest rate derivatives	$ 135	70
Interest Rate Swap No. 2 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives	$ 0	0
Interest Rate Swap No. 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative, term of contract	10 years
Fair value of interest rate derivatives	$ (70)	(492)
Fair value of interest rate derivatives	70	492
Interest Rate Swap No. 1 [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives	$ 0	0
Interest Rate Swap No. 1 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative, term of contract	10 years
Fair value of interest rate derivatives	$ 70	492
Interest Rate Swap No. 1 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives	$ 0	$ 0