Acquisitions (Pro forma results) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012 Actual Results [Member]	Sep. 30, 2011 Pro Forma [Member]	Jun. 30, 2012 Pro Forma [Member]	Sep. 30, 2011 Pro Forma [Member]
Revenue	$ 1,186,161	$ 1,644,736	$ 1,114,552	$ 3,678,070	$ 3,003,020
Net income from continuing operations	$ 95,184	$ 195,924	$ 111,083	$ 350,297	$ 249,724
Basic earnings per share	$ 0.61	$ 1.34	$ 0.72	$ 2.24	$ 1.62
Diluted earnings per share	$ 0.60	$ 1.32	$ 0.71	$ 2.21	$ 1.60