Acquisitions (Supplemental Pro Forma Results) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Actual Results [Member]
Revenue	$ 2,225,013
Net income from continuing operations	140,806
Basic earnings per share	$ 1.61
Diluted earnings per share	$ 1.59
Pro Forma [Member]
Revenue	4,858,464	4,214,617
Net income from continuing operations	$ 428,276	$ 390,209
Basic earnings per share	$ 2.70	$ 2.53
Diluted earnings per share	$ 2.70	$ 2.49