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Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 2,100		$ 1,100		$ 4,344	$ 2,117
Proceeds from stock options exercised					$ 702	$ 1,250
Shares withheld for employee taxes					6,927	5,208
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes		7,000		5,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	1,100		700		$ 2,100	$ 1,500
Total income tax benefit recognized related to restricted stock awards	900		500		$ 2,100	700
Compensation cost recognition weighted average period					2 years
Share-based compensation arrangement, fair value of awards vested					$ 6,700	$ 3,200
Shares granted in period					21,000	41,000
Shares vested in period					25,000	29,000
Unrecognized compensation costs	7,000				$ 7,000
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	200				$ 200
Compensation cost recognition weighted average period					1 year 7 months 6 days
Weighted-average remaining contractual life of options outstanding					5 years 3 months 18 days
Aggregate intrinsic value of options outstanding	11,400				$ 11,400
Weighted-average remaining contractual life of options exercisable					4 years 10 months 24 days
Aggregate intrinsic value of options exercisable	$ 9,100				$ 9,100
Intrinsic value of options exercised					$ 2,900	$ 900
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognition weighted average period					1 year 10 months 24 days
Share-based compensation arrangement shares to be issued	55,345				55,345
Unrecognized compensation costs	$ 6,800				$ 6,800
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		200		$ 1,100	$ 300
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			$ 200		$ 800	$ 300
Shares granted in period					25,999	25,738
Granted in 2020 [Member] \| Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	400
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	$ 200				$ 300
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