Summary of Significant Accounting Policies - Property and Equipment and Other Capitalized Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 39,003	$ 35,006
Less: accumulated depreciation and amortization	(28,102)	(25,220)
Property and equipment, net	10,901	9,786
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,266	1,554
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,201	3,863
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,844	2,887
Internal-use software and website development costs
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 29,692	$ 26,702

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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