Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 period	Dec. 31, 2013	Dec. 31, 2012
Employee Benefit [Line Items]
Defined Benefit Plan, Business Combinations and Acquisitions, Benefit Obligation	$ 511,000	$ 3,398,000
Number of Look-back Period Under Employee Stock Purchase Plan	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	34,168	32,598	39,393
Stock Issued During Period, Value, Employee Stock Purchase Plan	904,000	686,000	725,000
Shares Available For Purchase Under Employee Stock Purchase Plan	541,744
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	16,423,000	11,616,000
Change in actuarial loss	0	2,212,000
Benefit expense	1,325,000	1,880,000
Benefit payments	(1,718,000)	(2,683,000)
Balance at end of year	16,541,000	16,423,000	11,616,000
Pension Plan [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Service Period	6 months
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	2,000,000	1,900,000	1,400,000
Pension Plan [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age	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	6 months
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	4,400,000	4,000,000	2,900,000
Deferred Profit Sharing [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age	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	4,800,000	4,700,000
Deferred Compensation Arrangement with Individual, Compensation Expense	588,000	458,000	677,000
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	5.10%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Normal Retirement Age	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]
2015	975,000
2016	994,000
2017	1,088,000
2018	1,349,000
2019	1,384,000
2020 through 2024	9,580,000
Total	$ 15,370,000