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Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended		18 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 1,300		$ 830		$ 2,245	$ 1,635
Compensation cost recognition weighted average period					2 years 3 months
Share-based compensation, shares authorized under stock option plans, exercise price range, lower range limit					$ 26.52
Share-based compensation, shares authorized under stock option plans, exercise price range, upper range limit					$ 171.68
Share-based compensation arrangement by share-based payment award, options, grants in period, weighted average grant date fair value						$ 18.08
Proceeds from stock options exercised					$ 279	$ 62
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes		1,000		3,000	1,000	3,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	791		600		$ 1,500	$ 1,200
Total income tax benefit recognized related to restricted stock awards	385		546		$ 1,200	1,500
Compensation cost recognition weighted average period					2 years 1 month 24 days
Award vesting period					5 years
Share-based compensation arrangement, fair value of awards vested					$ 4,000	$ 7,400
Shares vested in period					31,000	85,000
Unrecognized compensation costs	3,900				$ 3,900		$ 3,900
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	700				$ 700		700
Compensation cost recognition weighted average period					2 years 11 months 1 day
Weighted-average remaining contractual life of options outstanding					7 years 7 months 9 days
Aggregate intrinsic value of options outstanding	7,500				$ 7,500		7,500
Weighted-average remaining contractual life of options exercisable					6 years 10 months 6 days
Aggregate intrinsic value of options exercisable	$ 4,600				$ 4,600		$ 4,600
Intrinsic value of options exercised					$ 1,000	$ 1,400
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement shares to be issued	291,080				291,080		291,080
Unrecognized compensation costs	$ 2,500				$ 2,500		$ 2,500
Performance Shares [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	151		151		303	303
Shares vested 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	$ 202				$ 292
Shares vested in period	17,780				17,780
Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 75		$ 79		$ 151	$ 152
Shares vested in period	63,300		63,300		63,300	63,300
Minimum [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					3 years
Maximum [Member] \| Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period					10 years