CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Loss	Total
Balances at Dec. 31, 2014	$ 277	$ 303,045	$ 338,810	$ (57,770)	$ (23,479)	$ 560,883
Balances (in shares) at Dec. 31, 2014	27,722			1,678
Increase (Decrease) in Stockholders' Equity
Net income			44,854			44,854
Other comprehensive income (loss), net of tax					(4,017)	(4,017)
Issuance of common stock under share-based compensation plans	$ 2	(2)
Issuance of common stock under share-based compensation plans (in shares)	216
Tax effect of share-based compensation plans		(1,419)				(1,419)
Share-based compensation expense		8,029				8,029
Purchase of treasury stock				$ (12,765)		(12,765)
Purchase of treasury stock (in shares)				402
Dividends declared on common stock			(6,837)			(6,837)
Balances at Dec. 31, 2015	$ 279	309,653	376,827	$ (70,535)	(27,496)	588,728
Balances (in shares) at Dec. 31, 2015	27,938			2,080
Increase (Decrease) in Stockholders' Equity
Net income			18,652			18,652
Other comprehensive income (loss), net of tax					4,079	4,079
Issuance of common stock under share-based compensation plans	$ 3	(3)
Issuance of common stock under share-based compensation plans (in shares)	236
Tax effect of share-based compensation plans		(2,322)				(2,322)
Share-based compensation expense		7,588				7,588
Purchase of treasury stock				$ (9,510)		(9,510)
Purchase of treasury stock (in shares)				485
Dividends declared on common stock			(8,318)			(8,318)
Balances at Dec. 31, 2016	$ 282	315,318	386,917	$ (80,045)	(23,417)	599,055
Balances (in shares) at Dec. 31, 2016	28,174			2,565
Increase (Decrease) in Stockholders' Equity
Cumulative effect of change in accounting principle (see Note B) | Adjustment | ASC Topic 718, Compensation – Stock Compensation		402	(244)			158
Net income			59,726			59,726
Other comprehensive income (loss), net of tax					2,843	2,843
Issuance of common stock under share-based compensation plans	$ 3	(3)
Issuance of common stock under share-based compensation plans (in shares)	322
Tax effect of share-based compensation plans		(2,837)				(2,837)
Share-based compensation expense		6,958				6,958
Purchase of treasury stock				$ (6,019)		(6,019)
Purchase of treasury stock (in shares)				287
Dividends declared on common stock			(8,264)			(8,264)
Balances at Dec. 31, 2017	$ 285	$ 319,436	$ 438,379	$ (86,064)	$ (20,574)	$ 651,462
Balances (in shares) at Dec. 31, 2017	28,496			2,852