Acquisitions (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Schedule of unaudited proforma information
Revenue - As reported	$ 1,573,295	$ 1,570,720	$ 4,673,431	$ 4,509,440
Net earnings - As reported	75,091	56,524	156,135	121,682
Net earnings per common share:
Basic - As reported	$ 1.47	$ 1.10	$ 3.06	$ 2.37
Diluted - As reported	$ 1.47	$ 1.10	$ 3.04	$ 2.35
Hill Hire [Member]
Schedule of unaudited proforma information
Revenue - Pro forma				4,577,010
Net earnings - Pro forma				$ 136,754
Net earnings per common share:
Basic - Pro forma				$ 2.66
Diluted - Pro forma				$ 2.64