Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (41,861,561)	$ (38,738,292)
Intangible assets, net	17,922,282	15,686,954
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	28,146,000	22,790,000
Accumulated amortization	(19,974,000)	(17,121,000)
Intangible assets, net	8,172,000	5,669,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(9,263,000)	(8,328,000)
Intangible assets, net	4,837,000	5,772,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,538,000	14,735,000
Accumulated amortization	(12,624,000)	(10,669,000)
Intangible assets, net	4,914,000	4,066,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	0	2,800,000
Accumulated amortization	0	(2,620,000)
Intangible assets, net	$ 0	$ 180,000