Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2011 period	Dec. 31, 2010	Dec. 31, 2009
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	39,989	35,806	55,443
Stock Issued During Period, Value, Employee Stock Purchase Plan	$ 690,000	$ 614,000	$ 578,000
Shares Available For Purchase Under Employee Stock Purchase Plan	647,903
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balance at beginning of year	10,363,000	9,947,000
Change in actuarial loss	329,000	(78,000)
Benefit expense	987,000	928,000
Benefit payments	(442,000)	(434,000)
Balance at end of year	11,237,000	10,363,000	9,947,000
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	1,175,000	866,000	748,000
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	2,600,000	1,200,000	0
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	4,400,000	4,000,000
Deferred Compensation Arrangement with Individual, Compensation Expense	655,000	750,000	530,000
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	5.30%	5.90%
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, Estimated Future Benefit Payments [Abstract]
2012	510,000
2013	526,000
2014	555,000
2015	572,000
2016	803,000
2017 through 2021	5,864,000
Total	$ 8,830,000