Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (41,550,241)	$ (38,738,292)
Intangible assets, net	16,986,371	15,686,954
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	25,511,000	22,790,000
Accumulated amortization	(18,391,000)	(17,121,000)
Intangible assets, net	7,120,000	5,669,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(8,797,000)	(8,328,000)
Intangible assets, net	5,303,000	5,772,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	16,125,000	14,735,000
Accumulated amortization	(11,591,000)	(10,669,000)
Intangible assets, net	4,534,000	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	(2,771,000)	(2,620,000)
Intangible assets, net	$ 29,000	$ 180,000