Stock Option Plan - Summary of Option Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Shares
Outstanding at January 1 (in shares)	1,768,375	1,601,250	1,502,670
Granted (in shares)	253,500	248,000	250,500
Exercised (in shares)	0	(26,875)	(64,920)
Expired/Forfeited (in shares)	(201,875)	(54,000)	(87,000)
Outstanding December 31 (in shares)	1,820,000	1,768,375	1,601,250
Exercisable (in shares)	1,177,375	1,237,250	1,098,500
Weighted Average Exercise Price
Outstanding at January 1 (in usd per share)	$ 51.28	$ 51.73	$ 52.86
Granted (in usd per share)	33.79	47.90	43.89
Exercised (in usd per share)	0	44.44	45.07
Expired/Forfeited (in usd per share)	46.20	52.60	53.60
Outstanding December 31 (in usd per share)	49.41	51.28	51.73
Exercisable (in usd per share)	52.52	$ 52.76	$ 53.22
Intrinsic value of options exercised		$ 0.2	$ 0.4
Closing price (in usd per share)	$ 39.27
Weighted average remaining life of options exercisable	4 years
Weighted average remaining life of options outstanding	5 years 3 months 18 days

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.