Other Retirement Plans (Multi-Employer Pension Plans Company Contributions in Excess of Five Percent of Total Plan Contributions) (Details)	12 Months Ended
	Dec. 31, 2011
Pipeline Industry Pension Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Multi-employer pension plans, company contributions in excess of five percent, plan years	2010
Laborers Local Union No. 158 Pension Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Multi-employer pension plans, company contributions in excess of five percent, plan years	2010
International Brotherhood of Electrical Workers Local 769 Management Pension Plan A [Member]
Defined Benefit Plan Disclosure [Line Items]
Multi-employer pension plans, company contributions in excess of five percent, plan years	2010
Minnesota Teamsters Construction Division Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Multi-employer pension plans, company contributions in excess of five percent, plan years	2010, 2009
Laborers Pension Fund (Roanoke, Virginia) [Member]
Defined Benefit Plan Disclosure [Line Items]
Multi-employer pension plans, company contributions in excess of five percent, plan years	2009