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Basis of Presentation and Significant Accounting Policies - Schedule of Intangible Assets (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
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Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | $ 181,921 | $ 172,730 | $ 209,992
Accumulated amortization | (33,000) | (25,168) | (25,146)
Net amortized intangible assets | 148,921 | 147,562 | 184,846
Technical support agreement |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 68,785 | 67,423 | 64,749
Accumulated amortization | (7,227) | (4,153) | (1,173)
Customer relationships |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 39,954 | 39,555 | 38,771
Accumulated amortization | (15,996) | (13,841) | (11,767)
Unpatented technology |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 37,529 | 36,785 | 35,327
Accumulated amortization | (4,584) | (2,805) | (1,194)
Favorable operating leases |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 0 | 0 | 35,161
Accumulated amortization | 0 | 0 | (1,295)
CNSC class 1B nuclear facility license |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 26,528 | 26,002 | 24,971
Accumulated amortization | (3,573) | (2,635) | (1,698)
Acquired backlog |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 7,487 | 0 | 8,079
Accumulated amortization | (1,248) | 0 | (6,581)
Patented technology |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 780 | 765 | 734
Accumulated amortization | (286) | (212) | (136)
All other |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Amortized intangible assets | 858 | 2,200 | 2,200
Accumulated amortization | (86) | (1,522) | (1,302)
NRC category 1 license |  |  |
Schedule Of Amortized And Unamortized Intangible Assets [Line Items] |  |  |
Unamortized intangible assets | $ 43,830 | $ 43,830 | $ 43,830

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