Intangible Assets (Details) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Identified intangible assets including amounts of accumulated amortization
Accumulated amortization	$ (26,409,134)	$ (24,067,250)
Total	16,122,120	16,332,596
Database [Member]
Identified intangible assets including amounts of accumulated amortization
Intangible assets, gross	16,199,000	15,175,000
Accumulated amortization	(12,440,000)	(11,691,000)
Total	3,759,000	3,484,000
Customer relationships [Member]
Identified intangible assets including amounts of accumulated amortization
Intangible assets, gross	14,100,000	14,100,000
Accumulated amortization	(5,932,000)	(5,444,000)
Total	8,168,000	8,656,000
Web site [Member]
Identified intangible assets including amounts of accumulated amortization
Intangible assets, gross	9,432,000	8,325,000
Accumulated amortization	(6,174,000)	(5,220,000)
Total	3,258,000	3,105,000
Acquired below market lease [Member]
Identified intangible assets including amounts of accumulated amortization
Intangible assets, gross	2,800,000	2,800,000
Accumulated amortization	(1,863,000)	(1,712,000)
Total	$ 937,000	$ 1,088,000