Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013 Reporting_Unit Customer Segment	Dec. 31, 2012 Customer	Dec. 31, 2011 Customer
Significant Accounting Policies [Line Items]
Revenue recognition period	less than six months
Useful life	2 years 8 months 12 days
Number of reporting segment	1
Number of reporting unit	1
Intangible assets with indefinite lives	$ 0	$ 0
Depreciation expense	3,823,000	3,279,000	2,759,000
Write off of fully depreciated assets no longer in service	2,700,000	800,000	1,300,000
Capitalized internal-use software and website development costs	$ 3,600,000	$ 3,000,000	$ 3,200,000
Number of customers represented 10% or more of total accounts receivable	0	0
Number of customers accounted for Specific revenue	0	1	1
Specific account receivable	10.00%	10.00%
Sales [Member]
Significant Accounting Policies [Line Items]
Percentage of revenue accounted by major customer	10.00%	12.00%	12.80%
Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life	2 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life	10 years