Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 period	Dec. 31, 2011	Dec. 31, 2010
Employee Benefit [Line Items]
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	39,393	39,989	35,806
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 725,000	$ 690,000	$ 614,000
Shares Available For Purchase Under Employee Stock Purchase Plan	608,510
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	11,237,000	10,363,000
Change in actuarial loss	(80,000)	329,000
Benefit expense	1,017,000	987,000
Benefit payments	(558,000)	(442,000)
Balance at end of year	11,616,000	11,237,000	10,363,000
Defined Contribution Pension [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	1,400,000	1,200,000	866,000
Defined Contribution Pension [Member] | Minimum [Member]
Employee Benefit [Line Items]
Deferred Compensation Arrangement with Individual, Eligible Age	18
Defined Contribution Pension [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	2,900,000	2,600,000	1,200,000
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	4,700,000	4,400,000
Deferred Compensation Arrangement with Individual, Compensation Expense	677,000	655,000	750,000
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%	5.30%
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]
2013	763,000
2014	758,000
2015	780,000
2016	917,000
2017	1,049,000
2018 through 2022	6,583,000
Total	$ 10,850,000