Employee Benefit Plans (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation	$ 570,027	$ 420,783	$ 395,833
Number of days of severance paid per year of service	10 days
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to benefit plan	6,600,000	6,000,000	6,000,000
Union Health and Welfare Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit costs and employer contributions	4,300,000	3,700,000	3,700,000
Non-Union Health And Welfare Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit costs and employer contributions	2,500,000	2,400,000	2,200,000
Money Purchase Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions to benefit plan	$ 141,000	$ 128,700	$ 124,100
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of days of severance paid	130 days
Number of years of service severance paid	13 years