CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Capital Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning Balance at Dec. 31, 2013	$ 555,527	$ 17,855	$ 110,577	$ 438,545	$ (11,450)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	14,580			14,580
Other comprehensive income (loss)	(158)				(158)
Stock options exercised	10,539	233	10,306
Shares issued for employees stock purchase plan	335	10	325
Shares issued for restricted stock	(687)	22	(709)
Stock-based compensation expense	1,758		1,758
Ending Balance at Mar. 31, 2014	$ 581,894	$ 18,120	$ 122,257	$ 453,125	$ (11,608)