Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (43,048,635)	$ (38,738,292)
Intangible assets, net	17,594,474	15,686,954
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	26,849,000	22,790,000
Accumulated amortization	(19,152,000)	(17,121,000)
Intangible assets, net	7,697,000	5,669,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(9,030,000)	(8,328,000)
Intangible assets, net	5,070,000	5,772,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	16,893,000	14,735,000
Accumulated amortization	(12,066,000)	(10,669,000)
Intangible assets, net	4,827,000	4,066,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,800,000	2,800,000
Accumulated amortization	(2,800,000)	(2,620,000)
Intangible assets, net	$ 0	$ 180,000