Segment Information - Revenue From External Customers Based Major Categories (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Geographical Areas [Line Items]
Revenue	$ 313,564	$ 338,160	$ 425,940
SDI [Member]
Disclosure Of Geographical Areas [Line Items]
Revenue	$ 15,600	$ 7,600	$ 16,700

The income arising in the course of an entity's ordinary activities. Income is increases in assets, or decreases in liabilities, that result in increases in equity, other than those relating to contributions from holders of equity claims.

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+ Details