Intangible Assets - Summary of Identified Intangible Assets (Detail) - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (36,090,371)	$ (33,589,746)
Total	14,505,614	14,681,410
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	20,749,000	19,435,000
Accumulated amortization	(16,007,000)	(15,018,000)
Total	4,742,000	4,417,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(7,855,000)	(7,379,000)
Total	6,245,000	6,721,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	12,947,000	11,936,000
Accumulated amortization	(9,760,000)	(8,876,000)
Total	3,187,000	3,060,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,800,000	2,800,000
Accumulated amortization	(2,469,000)	(2,317,000)
Total	$ 331,000	$ 483,000