Overview and Basis of Presentation - Schedule of Total Advertising Costs Included in Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Direct Salaries and Related Costs [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Customer-acquisition advertising costs	$ 12,104	$ 9,967
General and Administrative [Member]
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Customer-acquisition advertising costs	$ 18	$ 27

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 720
-SubTopic 35
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

Name:	us-gaap_AdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration