Stock-Based Compensation Plans (Summary of Stock Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022
Common Shares
Outstanding at beginning of the period (in shares)	68,093	193,447
Granted (in shares)	0	0
Exercised (in shares)	(54,218)	(83,507)
Forfeited or canceled (in shares)	0	(1,430)
Outstanding at end of the period (in shares)	13,875	108,510
Exercisable (in shares)	13,875	108,510
Weighted Average Strike Price
Outstanding at beginning of period (usd per share)	$ 41.14	$ 41.62
Granted (usd per share)	0	0
Exercised (usd per share)	40.87	42.39
Forfeited or canceled (usd per share)	0	40.87
Outstanding at end of period (usd per share)	42.18	41.04
Exercisable (usd per share)	$ 42.18	$ 41.04
Stock Options Additional Disclosures
Remaining contractual term, outstanding	4 years 6 months	1 year 2 months 12 days
Remaining contractual term, exercisable	4 years 6 months	1 year 2 months 12 days
Intrinsic value, outstanding	$ 422	$ 4,244
Intrinsic value, exercisable	$ 422	$ 4,244

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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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Gross number of share options (or share units) granted during the period.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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