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Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Finite Lived Intangible Assets [Line Items] |  |
Cost | $ 56,601 | $ 10,801
Accumulated amortization | (13,757) | (9,554)
Net book value | 42,844 | 1,247
Indefinite, cost | 5,871 | 5,871
Indefinite, net book value | 5,871 | 5,871
Total, cost | 62,472 | 16,672
Total, accumulated amortization | (13,757) | (9,554)
Total, net book value | $ 48,715 | $ 7,118
Customer Relationships [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 8 years | 11 years
Average remaining life in years | 7 years 6 months | 6 years 9 months 18 days
Cost | $ 50,244 | $ 10,644
Accumulated amortization | (11,713) | (9,510)
Net book value | $ 38,531 | $ 1,134
Customer Relationships [Member] | Minimum [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 8 years |
Customer Relationships [Member] | Maximum [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 11 years |
Non-compete Agreements [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 5 years | 5 years
Average remaining life in years | 4 years 6 months | 3 years 7 months 6 days
Cost | $ 3,257 | $ 157
Accumulated amortization | (336) | (44)
Net book value | $ 2,921 | $ 113
Customer Backlog [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 6 months |
Average remaining life in years | 1 month 6 days |
Cost | $ 1,900 |
Accumulated amortization | (1,633) |
Net book value | $ 267 |
Trade Name [Member] |  |
Finite Lived Intangible Assets [Line Items] |  |
Estimated useful life in years | 8 years |
Average remaining life in years | 7 years 6 months |
Cost | $ 1,200 |
Accumulated amortization | (75) |
Net book value | $ 1,125 |

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