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Basis of Presentation and Significant Accounting Policies - Changes in Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Beginning balance	$ 283,708	$ 275,502
Goodwill, Acquired During Period		5,753
Translation and other	1,794	2,453
Ending balance	285,502	283,708
Nuclear Operations Group
Goodwill [Roll Forward]
Beginning balance	110,939	110,939
Goodwill, Acquired During Period		0
Translation and other	0	0
Ending balance	110,939	110,939
Nuclear Services Group
Goodwill [Roll Forward]
Beginning balance	127,769	119,563
Goodwill, Acquired During Period		5,753
Translation and other	1,794	2,453
Ending balance	129,563	127,769
Nuclear Services Group
Goodwill [Roll Forward]
Beginning balance	45,000	45,000
Goodwill, Acquired During Period		0
Translation and other	0	0
Ending balance	$ 45,000	$ 45,000

X

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

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-Topic 350
-SubTopic 20
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
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-Section 55
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X

- Definition

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

+ References

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-Publisher FASB
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-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
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- Definition

Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

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- Definition

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+ References

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