Aggregate Purchase Price of Acquisitions (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Business Acquisition [Line Items]
Cash	$ 479,661	$ 190,430	$ 311,891
Promissory notes	38,461	77,760	38,090
Deferred consideration	11,695	2,474	0
Contingent consideration	8,182	16,061	0
Total purchase price	$ 537,999	$ 286,725	$ 349,981

Fair Value of the liabilities incurred by the acquirer to former owners of the acquiree, including the fair value of any contingent consideration. If liabilities transferred as consideration remain within the combined entity after the business combination (for example, because the assets or liabilities were transferred to the acquiree rather than to its former owners), and the acquirer therefore retains control of them; in that situation, the acquirer measures those liabilities at their carrying amounts immediately before the acquisition date.

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