Leases - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Capital Lease Obligations [Member] \| Computer Hardware and Related Equipment [Member]
Capital Leased Assets [Line Items]
Gross amount of assets under capital leases	$ 5.5	$ 7.3

Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=84164758&loc=d3e45014-112735

Name:	us-gaap_CapitalLeasedAssetsGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant