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Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 1,100		$ 1,300		$ 2,117	$ 2,245
Proceeds from stock options exercised					$ 1,250	$ 279
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes		5,000		1,000	0.0	0.0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	700		800		$ 1,500	$ 1,500
Total income tax benefit recognized related to restricted stock awards	500		400		$ 700	1,200
Compensation cost recognition weighted average period					1 year 10 months 24 days
Share-based compensation arrangement, fair value of awards vested					$ 3,200	$ 4,000
Shares granted in period					41,000	28,000
Shares vested in period					29,000	31,000
Unrecognized compensation costs	5,600				$ 5,600
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	300				$ 300
Compensation cost recognition weighted average period					2 years 3 months 18 days
Weighted-average remaining contractual life of options outstanding					6 years 3 months 18 days
Aggregate intrinsic value of options outstanding	6,300				$ 6,300
Weighted-average remaining contractual life of options exercisable					5 years 9 months 18 days
Aggregate intrinsic value of options exercisable	$ 4,900				$ 4,900
Intrinsic value of options exercised					$ 900	$ 1,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognition weighted average period					2 years 2 months 12 days
Share-based compensation arrangement shares to be issued	41,352				41,352
Shares vested in period							273,300
Unrecognized compensation costs	$ 3,400				$ 3,400
Performance Shares [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation			200			$ 300
Shares granted in period						210,000
Performance Shares [Member] \| Certain Key Executive [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation						$ 200
Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation			100
Shares granted in period						63,300
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	200		$ 200		$ 300	$ 300
Shares granted in period					15,821	17,780
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					$ 300
Shares granted in period					25,531
Granted in 2020 [Member] \| Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 200
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					$ 171.68
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