Intangible Assets - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	$ 4,828,452	$ 4,696,939	$ 4,629,394
Database [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset	2,286,000	1,974,000
Amortization expense for intangible assets	1,780,000	1,547,000	1,907,000
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	962,000	973,000	982,000
Website [Member]
Finite-Lived Intangible Assets [Line Items]
Amount capitalized to intangible asset	1,537,000	2,077,000
Amortization expense for intangible assets	1,784,000	1,875,000	1,436,000
Acquired Below Market Lease [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense for intangible assets	$ 303,000	$ 302,000	$ 304,000