Additional Financial Information - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Apr. 30, 2011 Contractual Arrangements and Customer Lists	Sep. 30, 2012 Contractual Arrangements and Customer Lists	Apr. 30, 2011 Marketing Intangibles	Apr. 30, 2011 Customer Lists	Apr. 30, 2011 Noncompete Agreements	Sep. 30, 2012 Acquired Finite Lived Intangible Assets	Sep. 30, 2011 Acquired Finite Lived Intangible Assets	Sep. 30, 2012 Acquired Finite Lived Intangible Assets	Sep. 30, 2011 Acquired Finite Lived Intangible Assets
Supplemental Financial Information [Line Items]
Depreciation and amortization expense	$ 1,126,000	$ 986,000	$ 3,234,000	$ 2,886,000
Contingent liability, performance period						2 years		2 years
Fair value of acquired intangible assets						9,700,000			7,800,000	1,900,000
Acquisition of intangible assets, useful life									6 years	2 years
Interest expense	42,000	334,000	428,000	1,150,000			300,000
Amortization expense for purchased intangibles	565,000	2,720,000	3,450,000	6,376,000							600,000	2,700,000	3,500,000	6,400,000
Goodwill	10,154,000		10,154,000		3,092,000
Goodwill acquired			$ 7,100,000