Acquisitions - Additional Information (Detail) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) Client_List shares	Mar. 31, 2017 USD ($) Client_List shares
Business Acquisition, Contingent Consideration [Line Items]
Increase in fair value of contingent consideration	$ 1.6	$ 0.6
Consideration paid in cash	$ 2.9	$ 2.9
Number of common stock issued \| shares	0	47,000
Acquisition of Client Lists [Member]
Business Acquisition, Contingent Consideration [Line Items]
Number of client list purchased \| Client_List	0	0

Amount of cash outflow, not made soon after acquisition date of business combination, to settle contingent consideration liability up to amount recognized at acquisition date, including, but not limited to, measurement period adjustment and less amount paid soon after acquisition date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration