Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	$ 1,765,000	$ 1,498,000	$ 5,134,125	$ 4,310,343
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset	1,363,000	1,338,000	4,140,000	4,059,000
Amortization expense for intangible assets	951,000	761,000	2,740,000	2,031,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	228,000	233,000	690,000	702,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset	762,000	768,000	2,513,000	2,158,000
Amortization expense for intangible assets	$ 586,000	475,000	$ 1,704,000	1,397,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets		$ 29,000		$ 180,000