Stock-Based Compensation Plans (Summary of Stock Option Activity) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Common Shares
Common shares, outstanding at beginning of the period (in shares)	193,447	520,663
Common shares, granted (in shares)	0	0
Common shares, exercised (in shares)	(79,376)	(208,579)
Common shares, forfeited or canceled (in shares)	(771)	(590)
Common shares, outstanding at end of the period (in shares)	113,300	311,494
Common shares, exercisable (in shares)	113,300	309,945
Weighted Average Strike Price
Weighted average strike price, outstanding at beginning of period (usd per share)	$ 41.62	$ 42.47
Weighted average strike price, granted (usd per share)	0	0
Weighted average strike price, exercised (usd per share)	42.32	42.96
Weighted average strike price, forfeited or canceled (usd per share)	40.87	46.86
Weighted average strike price, outstanding at end of period (usd per share)	41.13	42.14
Weighted average strike price, exercisable (usd per share)	$ 41.13	$ 42.11
Stock Options Additional Disclosures
Remaining contractual term, outstanding	1 year 4 months 24 days	1 year 9 months 18 days
Remaining contractual term, exercisable	1 year 4 months 24 days	1 year 9 months 18 days
Intrinsic value, outstanding	$ 5,869	$ 10,485
Intrinsic value, exercisable	$ 5,869	$ 10,441

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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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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock 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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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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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