Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) years period shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Employee Benefit [Line Items]
Number of Look-back Period Under Employee Stock Purchase Plan | period	2
Look-back Period Under Employee Stock Purchase Plan	6 months
Discount On Common Stock Under Employee Stock Purchase Plan, Percent	10.00%
Stock Issued During Period, Shares, Employee Stock Purchase Plans | shares	79,297	57,201	50,750
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 2,200	$ 2,100	$ 2,000
Shares Available For Purchase Under Employee Stock Purchase Plan | shares	223,859
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	$ 24,914	21,287
Change in actuarial loss	2,836	2,663
Benefit expense	1,887	1,930
Defined Benefit Plan, Benefit Obligation, Benefits Paid	2,235	966
Balance at end of year	27,402	24,914	21,287
Pension Plan
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contributions by Employer	$ 3,800	3,500	3,300
Pension Plan | Minimum
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age | years	18
Pension Plan | Maximum
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation	3.00%
Deferred Profit Sharing
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contribution To Plan By Employee, Percent Of Eligible Compensation	75.00%
Deferred Compensation Arrangement with Individual, Contribution Requirements, Matching Percent	50.00%
Deferred Compensation Arrangement with Individual, Contributions by Employer	$ 8,100	7,300	7,000
Deferred Profit Sharing | Minimum
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age | years	18
Deferred Profit Sharing | Maximum
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation	3.00%
ESP Plan
Employee Benefit [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date	90.00%
Unit Plans
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Vesting Period	10
Deferred Compensation Arrangement with Individual, Benefit Period	10
Deferred Compensation Arrangement with Individual, Recorded Liability	$ 4,000	4,000
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 488	$ 415	$ 337
SERP
Employee Benefit [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.51%	3.34%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Normal Retirement Age | years	65
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Annual Cost Of Living Benefit Adjustment	2.00%
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2021	$ 1,111
2022	1,117
2023	1,203
2024	1,520
2025	1,717
2026 through 2030	7,784
Total	$ 14,452