Stockholders' Equity Common Stock - Stock Based Compensation - Additional Information (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Equity [Abstract]
Unrecognized stock- based compensation cost	$ 28,102
Weighted average period over which unrecognized compensation cost is expected to be recognized	2 years 1 month 20 days

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration