Additions, Payments, and Net Changes, as well as Interest Expense Accretion on Estimated Acquisition Earn-Out Payables (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Business Combinations [Abstract]
Beginning balance	$ 48,918	$ 57,997	$ 52,987	$ 47,715
Additions to estimated acquisition earn-out payables	955	2,136	2,787	15,055
Payments for estimated acquisition earn-out payables	(2,518)	(2,743)	(10,597)	(4,388)
Subtotal	47,355	57,390	45,177	58,382
Change in fair value on estimated acquisition earn-out payables	(1,146)	240	10	(1,966)
Interest expense accretion	481	618	1,503	1,832
Net change in earnings from estimated acquisition earn-out payables	(665)	858	1,513	(134)
Ending balance	$ 46,690	$ 58,248	$ 46,690	$ 58,248