Defined Benefit Pension Plans - Fair Values of Plan Investments by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	$ 11,890	$ 12,834	$ 10,215
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	787	789
Guaranteed Insurance Contract, Type of Benefit [Domain]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	8,020	8,384
Securities (Assets) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	3,083	3,661
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	787	789
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	787	789
Fair Value, Inputs, Level 1 [Member] | Guaranteed Insurance Contract, Type of Benefit [Domain]
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	11,103	12,045	9,432
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] | Guaranteed Insurance Contract, Type of Benefit [Domain]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	8,020	8,384	7,011
Fair Value, Inputs, Level 3 [Member] | Securities (Assets) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan assets	$ 3,083	$ 3,661	$ 2,421