Summary of Fair Value of Plan Assets by Asset Category (Details) - USD ($) $ in Thousands	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 38,983		$ 33,124		$ 36,476
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	110		109
Not Subject to Leveling | ASU 2015-07
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	38,873		33,015
Balanced Fund
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	28,831	[1]	24,564	[2]
Balanced Fund | Not Subject to Leveling | ASU 2015-07
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	28,831	[1]	24,564	[2]
Fixed Income
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	10,042	[3]	8,451	[4]
Fixed Income | Not Subject to Leveling | ASU 2015-07
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	10,042	[3]	8,451	[4]
Cash
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	110		109
Cash | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair Value of Plan Assets	$ 110		$ 109

[1] This class comprises a diversified portfolio of global investments which seeks a balanced return between capital growth and fixed income and is allocated on a weighted average basis as follows: equities (32%), bonds (42%), other assets (19%) and cash (7%).

[2] This class comprises a diversified portfolio of global investments which seeks a balanced return between capital growth and fixed income and is allocated on a weighted average basis as follows: equities (42%), bonds (19%), other assets (38%) and cash (1%).

[3] This class comprises a diversified portfolio of global investments which seeks fixed income growth and is allocated on a weighted average basis as follows: bonds (92%), other assets (5%) and cash (3%).

[4] This class comprises a diversified portfolio of global investments which seeks long-term capital growth and is allocated on a weighted average basis as follows: bonds (86%) and cash (14%).