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Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 2,300		$ 2,100		$ 6,613	$ 4,243
Proceeds from stock options exercised					$ 811	$ 1,424
Shares withheld for employee taxes					7,226	5,432
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes	1,000	7,000		5,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 1,100		1,000		$ 3,200	$ 2,500
Total income tax benefit recognized related to restricted stock awards	100		300		$ 2,300	900
Compensation cost recognition weighted average period					1 year 9 months 18 days
Share-based compensation arrangement, fair value of awards vested					$ 6,900	$ 3,400
Shares granted in period					21,000	43,000
Shares vested in period					26,000	30,000
Unrecognized compensation costs	5,800				$ 5,800
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee service share based compensation nonvested awards total compensation cost not yet recognized	100				$ 100
Compensation cost recognition weighted average period					1 year 4 months 24 days
Weighted-average remaining contractual life of options outstanding					5 years
Aggregate intrinsic value of options outstanding	6,700				$ 6,700
Weighted-average remaining contractual life of options exercisable					4 years 7 months 6 days
Aggregate intrinsic value of options exercisable	$ 5,300				$ 5,300
Intrinsic value of options exercised					$ 3,300	$ 1,100
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognition weighted average period					1 year 8 months 12 days
Share-based compensation arrangement shares to be issued	55,345				55,345
Unrecognized compensation costs	$ 5,600				$ 5,600
Granted in 2019 [Member] \| Performance Shares [Member] \| Certain Key Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	400		500		$ 1,400	$ 800
Shares granted in period					15,834	16,637
Granted in 2020 [Member] \| Performance Shares [Member] \| Certain Key Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation			$ 600		$ 1,300	$ 900
Shares granted in period					25,999	27,525
Granted in 2020 [Member] \| Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	500
Granted in 2021 [Member] \| Performance Shares [Member] \| Certain Key Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 300				$ 700
Shares granted in period					13,512
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares authorized under stock option plans, exercise price range, lower range limit					$ 26.52
Minimum [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					3 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares authorized under stock option plans, exercise price range, upper range limit					$ 66.68
Maximum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					5 years
Maximum [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period					10 years