Allowance for Doubtful Accounts - Schedule of Allowance for Doubtful Activity Included in Accounts Receivable Net (Detail) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Valuation And Qualifying Accounts Disclosure [Line Items]
Balances, January 1	$ 763	$ 515	$ 446
Provision for doubtful accounts	2,590	1,705	1,375
Write-offs, net of recoveries	(1,961)	(1,457)	(1,306)
Balances, December 31	$ 1,392	$ 763	$ 515

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- Definition

Amount of valuation and qualifying accounts and reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09)
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690

+ Details

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- Definition

Amount of increase in valuation and qualifying accounts and reserves from charge to cost and expense.

+ References

+ Details

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- Definition

Amount of decrease in valuation and qualifying accounts and reserves.

+ References

+ Details

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