Derivative Financial Instruments - Summary of Non-designated Hedges (Detail) - Derivatives not designated as hedging instruments £ in Thousands, $ in Thousands	Sep. 30, 2023 GBP (£) derivative_instrument	Dec. 31, 2022 GBP (£) derivative_instrument	Dec. 31, 2022 AUD ($) derivative_instrument
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Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of Instruments	1	2	2
Notional Amount | £	£ 14,300	£ 109,076
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Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of Instruments	1	2	2
Notional Amount | £	£ 14,300	£ 109,076
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Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of Instruments		1	1
Notional Amount | $			$ 23,600
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Derivative Instruments and Hedging Activities Disclosures [Line Items]
Number of Instruments		1	1
Notional Amount | $			$ 23,600