Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - Norstel A B [Member] $ in Millions	Feb. 06, 2019 USD ($)
Subsequent Event [Line Items]
Equity interest percentage by parent	55.00%
Equity interest remaining percentage acquire subject to certain conditions	45.00%
Total consideration	$ 137.5

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
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