Business Combinations - Additions, Payments, and Net Changes, as well as Interest Expense Accretion on Estimated Acquisition Earn-Out Payables (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Business Combinations [Abstract]
Beginning balance	$ 48,806,000	$ 49,469,000	$ 43,058,000	$ 52,987,000
Additions to estimated acquisition earn-out payables	14,527,000	2,554,000	14,807,000	1,833,000
Payments for estimated acquisition earn-out payables	(10,814,000)	(3,761,000)	(11,429,000)	(8,080,000)
Subtotal	52,519,000	48,262,000	46,436,000	46,740,000
Change in fair value on estimated acquisition earn-out payables	(375,000)	159,000	5,228,000	1,156,000
Interest expense accretion	552,000	497,000	1,032,000	1,022,000
Net change in earnings from estimated acquisition earn-out payables	177,000	656,000	6,260,000	2,178,000
Ending balance	$ 52,696,000	$ 48,918,000	$ 52,696,000	$ 48,918,000