Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (46,995,686)	$ (41,861,561)
Intangible assets, net	19,441,536	17,922,282
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	32,286,000	28,146,000
Accumulated amortization	(22,714,000)	(19,974,000)
Intangible assets, net	9,572,000	8,172,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(9,953,000)	(9,263,000)
Intangible assets, net	4,147,000	4,837,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	20,051,000	17,538,000
Accumulated amortization	(14,328,000)	(12,624,000)
Intangible assets, net	$ 5,723,000	$ 4,914,000