Defined Benefit Pension Plans - Fair Values of Plan Investments by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	$ 12,665	$ 11,890	$ 12,834
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	926	787
Insurance Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	8,133	8,020
Securities (Assets) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	3,606	3,083
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	926	787
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	926	787
Fair Value, Inputs, Level 1 [Member] | Insurance Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	0	0
Fair Value, Inputs, Level 1 [Member] | Securities (Assets) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	0	0
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	11,739	11,103	12,045
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	0	0
Fair Value, Inputs, Level 3 [Member] | Insurance Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	8,133	8,020	8,384
Fair Value, Inputs, Level 3 [Member] | Securities (Assets) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	$ 3,606	$ 3,083	$ 3,661