Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) period years shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 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	50,750	38,387	50,116
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 2,000	$ 1,500	$ 1,800
Shares Available For Purchase Under Employee Stock Purchase Plan | shares	360,357
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	$ 20,553	26,263
Change in actuarial loss	(31)	(6,453)
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	148
Benefit expense	1,701	1,600
Defined Benefit Plan, Benefit Obligation, Benefits Paid	936	1,005
Balance at end of year	$ 21,287	20,553	26,263
Pension Plan [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Requisite Service Period	1 month
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	$ 3,300	2,700	2,400
Pension Plan [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age | years	18
Pension Plan [Member] | Maximum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation	3.00%
Deferred Profit Sharing [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Requisite Service Period	1 month
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	$ 7,000	5,700	5,100
Deferred Profit Sharing [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age | years	18
Deferred Profit Sharing [Member] | Maximum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation	3.00%
ESP Plan [Member]
Employee Benefit [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date	90.00%
Unit Plans [Member]
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	$ 4,200	4,600
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 337	$ 452	$ 467
SERP [Member]
Employee Benefit [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.30%	3.80%
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]
2019	$ 963
2020	1,971
2021	2,095
2022	1,135
2023	1,236
2024 through 2028	8,236
Total	$ 15,636