Fair Value of Assets and Liabilities - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Feb. 28, 2011
Fair Value Disclosures [Line Items]
Contingent consideration	$ 16,935,000	$ 16,935,000	$ 21,595,000	$ 1,100,000	$ 10,900,000	$ 9,600,000
Paid to the former shareholders	1,700,000	1,740,000
February 2011 Acquisition [Member]
Fair Value Disclosures [Line Items]
Contingent consideration included in earnings	3,500,000	3,500,000
June 2011 Acquisition [Member]
Fair Value Disclosures [Line Items]
Contingent consideration included in earnings	$ (600,000)	$ (600,000)