Employee Benefit Plans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) years period shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares
Employee Benefit [Line Items]
Defined Benefit Plan, Business Combinations and Acquisitions, Benefit Obligation	$ 0	$ 511
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	42,134	34,168	32,598
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 1,200	$ 904	$ 686
Shares Available For Purchase Under Employee Stock Purchase Plan | shares	499,610
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	$ 16,541	16,423
Change in actuarial loss	4,874	0
Defined Benefit Plan, Plan Amendments	2,617	0
Benefit expense	2,491	1,325
Benefit payments	(979)	(1,718)
Balance at end of year	$ 25,544	16,541	16,423
Pension Plan [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Service Period	3
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	$ 2,300	2,000	1,900
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, Service Period	3
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	$ 5,200	4,400	4,000
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, Recorded Liability	$ 4,900	4,800
Deferred Compensation Arrangement with Individual, Compensation Expense	$ 859	$ 588	$ 458
Unit Plans [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Vesting Period	4 years
Deferred Compensation Arrangement with Individual, Benefit Period	5 years
Unit Plans [Member] | Maximum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Vesting Period	10 years
Deferred Compensation Arrangement with Individual, Benefit Period	10 years
SERP [Member]
Employee Benefit [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.26%	5.10%
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	$ 994
2017	1,128
2018	1,510
2019	1,548
2020	2,568
2021 through 2025	10,492
Total	$ 18,240