Goodwill (Tables)

12 Months Ended

Dec. 31, 2011

Changes in Book Value of Goodwill

Changes in the book value of goodwill were as follows:

	Year ended December 31,
	2011			2010
Balance at January 1	$	4,091,307		$	3,951,196
Acquisitions		889,506			152,252
Divestitures		(9,837	)		(12,128	)
Impairment charge		(24,000	)		—
Other adjustments		—			(13	)
Balance at December 31	$	4,946,976		$	4,091,307