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, 2012	$ 438,397	$ 16,904	$ 74,272	$ 405,029	$ (57,808)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	38,305			38,305
Other comprehensive income (loss)	46,358				46,358
Stock options exercised	32,426	859	31,567
Stock issued to directors	0	15	(15)
Shares issued for employees stock purchase plan	734	24	710
Shares issued for restricted stock	(1,297)	53	(1,350)
Stock-based compensation expense	5,393		5,393
Ending 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)