CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2011	$ 338,256	$ 16,221	$ 52,738	$ 332,099	$ (62,802)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	68,685			68,685
Other comprehensive income (loss)	4,994				4,994
Stock options exercised	17,007	603	16,404
Stock issued to directors	0	15	(15)
Shares issued for employees stock purchase plan	809	27	782
Shares issued for restricted stock	(752)	38	(790)
Stock-based compensation expense	5,153		5,153
Ending Balance at Dec. 31, 2012	434,152	16,904	74,272	400,784	(57,808)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	37,761			37,761
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	555,527	17,855	110,577	438,545	(11,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	52,883			52,883
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	$ 581,963	$ 18,404	$ 137,225	$ 491,428	$ (65,094)