Shareholders' Equity - Additional Information (Details) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2021 £ / shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 £ / shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 $ / shares
Class of Stock [Line Items]
Deferred shares, multiple of amount paid up on ordinary shares				100
Purchase of treasury shares | $		$ 6.4
Cancellation of treasury shares | $		$ 0.0
Number of treasury shares held (in shares)				575,618		350,335
Cost of treasury shares held | $				$ 9.6		$ 4.0
June 2021 Share Buy-Back Program
Class of Stock [Line Items]
Number of ordinary shares repurchased (in shares)	297,678
Purchase of treasury shares | $	$ 6.4
Shares cancelled (in shares)	56,000
Cancellation of treasury shares | $	$ 0.7
Shares utilized (in shares)	16,395
Utilization of treasury shares | $	$ 0.1
Number of treasury shares held (in shares)				225,283
Ordinary shares
Class of Stock [Line Items]
Common stock, par value (in GBP per share) | (per share)			£ 0.50	$ 0.50	£ 0.50	$ 0.50	$ 0.50
Common stock, shares, outstanding, actively traded (in shares)				27,529,824		27,636,153
Ordinary shares | Own shares held by ESOP
Class of Stock [Line Items]
Common stock, par value (in GBP per share) | £ / shares			0.50		0.50
Employee stock ownership plan, shares held by trustees (in shares)				838,558		1,013,512
Deferred shares
Class of Stock [Line Items]
Common stock, par value (in GBP per share) | £ / shares			£ 0.0001		£ 0.0001