Business Combinations - Additions, Payments, and Net Changes, as well as Interest Expense Accretion on Estimated Acquisition Earn-Out Payables (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Business Combinations [Abstract]
Beginning balance	$ 43,058,000	$ 52,987,000
Additions to estimated acquisition earn-out payables	280,000	(721,000)
Payments for estimated acquisition earn-out payables	(615,000)	(4,319,000)
Subtotal	42,723,000	47,947,000
Change in fair value on estimated acquisition earn-out payables	5,603,000	997,000
Interest expense accretion	480,000	525,000
Net change in earnings from estimated acquisition earn-out payables	6,083,000	1,522,000
Ending balance	$ 48,806,000	$ 49,469,000