Business Combinations (Estimated Acquisition Earn-Out Payables) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Business Combination, Separately Recognized Transactions [Line Items]
Balance as of the beginning of the period	$ 57,997	$ 41,913	$ 47,715	$ 29,609
Additions to estimated acquisition earn-out payables	2,136	1,648	15,055	15,463
Payments for estimated acquisition earn-out payables	(2,743)	(2,290)	(4,388)	(5,267)
Sub Total	57,390	41,271	58,382	39,805
Change in fair value on estimated acquisition earn-out payables	240	(1,286)	(1,966)	(697)
Interest expense accretion	618	476	1,832	1,353
Net change in earnings from estimated acquisition earn-out payables	858	(810)	(134)	656
Balance as of June 30	$ 58,248	$ 40,461	$ 58,248	$ 40,461