Benefit Plans (Details) (USD $)	12 Months Ended							1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2000	Dec. 31, 2011 Pension Plan	Dec. 31, 2010 Pension Plan	Dec. 31, 2009 Pension Plan	Jan. 31, 2009 Health Plan	Dec. 31, 2011 Health Plan	Dec. 31, 2010 Health Plan	Dec. 31, 2009 Health Plan	Dec. 31, 2011 Pension Plan	Dec. 31, 2010 Pension Plan	Dec. 31, 2009 Pension Plan	Dec. 31, 2011 Health Plan	Dec. 31, 2010 Health Plan	Dec. 31, 2009 Health Plan	Dec. 31, 2011 Other plans	Dec. 31, 2010 Other plans	Dec. 31, 2009 Other plans
Multi-employer plans
Plan contributions	$ 14,294,000	$ 11,732,000	$ 10,661,000		$ 201,300,000	$ 193,300,000	$ 177,700,000		$ 843,200,000	$ 770,800,000	$ 705,500,000	$ 2,264,000	$ 1,835,000	$ 1,704,000	$ 6,919,000	$ 5,754,000	$ 5,319,000	$ 5,111,000	$ 4,143,000	$ 3,638,000
Employer contributions per quarter								1,950,000
401 (K) Plan
Employee contribution limit per calendar year (as a percent of compensation)	15.00%
Employer match of employee contributions of first specified percentage of annual compensation	50.00%	50.00%	50.00%	50.00%
Percentage of eligible compensation matched by employer	6.00%	6.00%	6.00%	4.00%
Matching contribution	$ 502,000	$ 450,000	$ 450,000