Business Combinations (Results Of Operations) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 2012 Acquisitions [Member]	Mar. 31, 2011 2012 Acquisitions [Member]	Mar. 31, 2011 2011 Acquisitions [Member]	Mar. 31, 2010 2011 Acquisitions [Member]
Business Acquisition [Line Items]
Total revenues			$ 304,916	$ 289,935	$ 262,979	$ 258,069
Income before income taxes			83,481	84,178	76,932	75,171
Net income			$ 49,846	$ 50,826	$ 46,451	$ 45,388
Net income per share, Basic			$ 0.35	$ 0.36	$ 0.33	$ 0.32
Net income per share, Diluted			$ 0.34	$ 0.35	$ 0.32	$ 0.32
Weighted average number of shares outstanding, Basic	139,001	138,351	139,001	138,351	138,351	137,623
Weighted average number of shares outstanding, Diluted	141,500	140,648	141,500	140,648	140,648	137,791