Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (52,906,758)	$ (48,892,725)
Intangible assets, net	19,285,197	19,474,411
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	35,877,000	33,538,000
Accumulated amortization	(25,840,000)	(23,705,000)
Intangible assets, net	10,037,000	9,833,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(10,634,000)	(10,182,000)
Intangible assets, net	3,466,000	3,918,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	22,215,000	20,729,000
Accumulated amortization	(16,433,000)	(15,006,000)
Intangible assets, net	$ 5,782,000	$ 5,723,000