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Share-based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended			36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	May 18, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 4,520	$ 3,124	$ 4,267
Proceeds from stock options exercised	$ 278	$ 547	$ 568
Share-based compensation arrangement shares to be issued					1,600,000
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes	128,000	7,000	44,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 2,900	$ 2,200	$ 3,400
Total income tax benefit recognized related to restricted stock awards	$ 7,500	2,500	2,100
Compensation cost recognition weighted average period	1 year 10 months 24 days
Award vesting period	5 years
Share-based compensation arrangement, fair value of awards vested	$ 4,700	$ 8,600	6,800
Shares granted in period	29,000	19,000
Shares vested in period	37,000	91,000
Unrecognized compensation costs	$ 2,700			$ 2,700
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	$ 500			500
Compensation cost recognition weighted average period	2 years 7 months 17 days
Weighted-average remaining contractual life of options outstanding	7 years 1 month 9 days
Aggregate intrinsic value of options outstanding	$ 5,700			5,700
Weighted-average remaining contractual life of options exercisable	6 years 4 months 2 days
Aggregate intrinsic value of options exercisable	$ 3,600			3,600
Award vesting period	3 years
Award expiration period	10 years
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
Intrinsic value of options exercised	$ 1,000	$ 4,100
Stock Options [Member] \| Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares withheld for employee taxes	1,000	6,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost recognition weighted average period	2 years
Shares granted in period	17,780
Unrecognized compensation costs	$ 1,600			1,600
Performance Shares [Member] \| Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation				$ 600
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	$ 300	$ 300	$ 300
Shares vested in period	63,300
Performance Shares [Member] \| Key Executives [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation	$ 700
Shares granted in period	17,780