Goodwill - Additional Information (Detail) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	May 01, 2018	Dec. 31, 2017
Goodwill Disclosure [Abstract]
Goodwill	$ 274,202,000		$ 19,022,000	$ 255,353,000
Goodwill, Period Increase (Decrease)	18,800,000
Impairment charges on goodwill	$ 0	$ 0

Goodwill Disclosure [Abstract]

No definition available.

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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
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-Section 45
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- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
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-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 28
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-Name Accounting Standards Codification
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- Definition

Amount of increase (decrease) of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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