Employee Benefits - Pension Plan Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	$ 122,344	$ 116,652	$ 101,765
Fair Value Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	122,344	116,652
Fair Value Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	1,563	1,831
Fair Value Measurements, Recurring | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	108,583	101,320
Fair Value Measurements, Recurring | Equity index mutual funds - international
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	3,332	3,066
Fair Value Measurements, Recurring | Domestic individual equities
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	8,866	10,435
Fair Value Measurements, Recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	122,344	116,652
Fair Value Measurements, Recurring | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	1,563	1,831
Fair Value Measurements, Recurring | Level 1 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	108,583	101,320
Fair Value Measurements, Recurring | Level 1 | Equity index mutual funds - international
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	3,332	3,066
Fair Value Measurements, Recurring | Level 1 | Domestic individual equities
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	8,866	10,435
Fair Value Measurements, Recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 2 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 2 | Equity index mutual funds - international
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 2 | Domestic individual equities
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 3
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 3 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 3 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 3 | Equity index mutual funds - international
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	0	0
Fair Value Measurements, Recurring | Level 3 | Domestic individual equities
Defined Benefit Plan Disclosure [Line Items]
Total Assets at Fair Value	$ 0	$ 0