Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) period years shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 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	50,116	42,134	34,168
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 1,800	$ 1,200	$ 904
Shares Available For Purchase Under Employee Stock Purchase Plan | shares	449,494
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	$ 25,544	16,541
Change in actuarial loss	62	4,874
Defined Benefit Plan, Plan Amendments	0	2,617
Benefit expense	2,201	2,491
Benefit payments	1,544	979
Balance at end of year	$ 26,263	25,544	16,541
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, Employer Contribution	$ 2,400	2,300	2,000
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, Employer Contribution	$ 5,100	5,200	4,400
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	$ 4,800	4,900
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 467	$ 859	$ 588
SERP [Member]
Employee Benefit [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.09%	4.26%
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 Payments, Fiscal Year Maturity [Abstract]
2016	$ 1,014
2017	1,510
2018	1,549
2019	2,569
2020	2,705
2021 through 2025	9,915
Total	$ 19,262