Summary of Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Fair Value, Measurement Inputs, Disclosure
Total, beginning of the period	$ 2,755	$ 9,727	$ 3,782	$ 8,515
Contingent consideration	221	2,400		5,700
Change in fair value of contingent consideration	(57)		138
Payment of contingent consideration	(735)	(614)	(1,736)	(2,702)
Total, end of the period	$ 2,184	$ 11,513	$ 2,184	$ 11,513