Revenue Recognition - Summary of Contract Assets Offset with Deferred Revenue Balances (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue Recognition [Abstract]
Gross deferred revenue	$ 58,779	$ 37,260	$ 39,544	$ 39,544
Gross contract assets	(35,791)		(9,984)
Deferred revenue, net	$ 22,988		$ 29,560	$ 22,897

Amount, before allowance for credit loss, of right to consideration in exchange for good or service transferred to customer, when right is conditioned on something other than passage of time.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130533-203044

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant