Intangible Assets - Summary of Identified Intangible Assets (Detail) (USD $)	Mar. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization	$ (29,917,266)	$ (28,764,189)
Total	15,612,310	15,687,117
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	17,745,000	17,149,000
Accumulated amortization	(13,651,000)	(13,238,000)
Total	4,094,000	3,911,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(6,658,000)	(6,417,000)
Total	7,442,000	7,683,000
Web Site [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	10,884,000	10,402,000
Accumulated amortization	(7,518,000)	(7,095,000)
Total	3,366,000	3,307,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible assets, gross	2,800,000	2,800,000
Accumulated amortization	(2,090,000)	(2,014,000)
Total	$ 710,000	$ 786,000