Intangible Assets - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Purchase of intangible assets		$ 8,508,597	$ 5,804,090	$ 3,822,745
Amortization expense for intangible assets		5,923,269	5,148,546	4,828,452
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset		5,356,000	3,355,000
Amortization expense for intangible assets		2,853,000	2,103,000	1,780,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets		935,000	949,000	962,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset		2,803,000	2,799,000
Amortization expense for intangible assets		1,955,000	1,793,000	1,784,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets		$ 180,000	$ 303,000	$ 303,000
Intellectual Property [Member] | Reis Portfolio CRE [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase of intangible assets	$ 700,000