CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Capital Stock/Capital Shares	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2013	$ 560,316	$ 17,855	$ 110,577	$ 443,334	$ (11,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,412			53,412
Other comprehensive income (loss)	(53,644)				(53,644)
Stock options exercised	20,513	465	20,048
Stock issued to directors	0	16	(16)
Shares issued for employees stock purchase plan	693	16	677
Shares issued for restricted stock	(1,542)	52	(1,594)
Stock-based compensation expense	7,533		7,533
Ending Balance at Dec. 31, 2014	587,281	18,404	137,225	496,746	(65,094)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	46,320			46,320
Other comprehensive income (loss)	(23,364)				(23,364)
Stock options exercised	6,967	175	6,792
Stock issued to directors	0	16	(16)
Shares issued for employees stock purchase plan	727	13	714
Shares issued for restricted stock	(2,740)	77	(2,817)
Shares repurchased	(39,993)	(728)	(39,265)
Tax shortfalls on share-based compensation	(259)		(259)
Stock-based compensation expense	9,643		9,643
Ending Balance at Dec. 31, 2015	584,582	17,957	112,017	543,066	(88,458)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,283			48,283
Other comprehensive income (loss)	(3,804)				(3,804)
Stock options exercised	4,143	95	4,048
Stock issued to directors	0	24	(24)
Shares issued for employees stock purchase plan	858	23	835
Shares issued for restricted stock	(1,377)	63	(1,440)
Shares repurchased	(7,995)	(141)	(7,854)
Tax adjustments on share-based compensation	(179)		(179)
Stock-based compensation expense	11,275		11,275
Ending Balance at Dec. 31, 2016	$ 635,786	$ 18,021	$ 118,678	$ 591,349	$ (92,262)