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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Business Combinations [Abstract]
Beginning balance	$ 49,469	$ 51,908	$ 52,987	$ 47,715
Additions to estimated acquisition earn-out payables	2,554	8,205	1,833	12,919
Payments for estimated acquisition earn-out payables	(3,761)	(1,512)	(8,080)	(1,645)
Subtotal	48,262	58,601	46,740	58,989
Change in fair value on estimated acquisition earn-out payables	159	(1,236)	1,156	(2,206)
Interest expense accretion	497	632	1,022	1,214
Net change in earnings from estimated acquisition earn-out payables	656	(604)	2,178	(992)
Ending balance	$ 48,918	$ 57,997	$ 48,918	$ 57,997