Financial Instruments (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, percentage bearing fixed interest, amount		$ 200,000
Long-term debt, percentage bearing variable interest, amount		104,000
Deferred compensation assets	[1]	40,518	$ 47,009
Deferred compensation plan, assets		40,518	47,009
Deferred compensation liability		31,000	34,081
Deferred compensation plan, liability		34,336	35,135
Interest Rate Swap No. 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives		$ 2,348	$ 1,054
Derivative, term of contract		10 years	10 years
Fair value of interest rate derivatives		$ (2,348)	$ (1,054)
Interest Rate Swap No. 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives		$ 988
Derivative, term of contract		5 years	5 years
Fair value of interest rate derivatives		$ (988)
Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deferred compensation assets	[1]	40,518	$ 47,009
Deferred compensation plan, assets		40,518	47,009
Deferred compensation liability		31,000	34,081
Deferred compensation plan, liability		34,336	35,135
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap No. 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives		$ 2,348	$ 1,054
Derivative, term of contract		10 years	10 years
Fair Value, Inputs, Level 2 [Member] | Interest Rate Swap No. 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of interest rate derivatives		$ 988
Derivative, term of contract		5 years	5 years
Interest Rate Swap [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, percentage bearing fixed interest, amount		$ 200,000
Long-term debt, percentage bearing variable interest, amount		$ 96,000

[1] Deferred compensation assets consist of the cash surrender value of life insurance policies and are intended to assist in the funding of the deferred compensation agreements.