CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Common Stock Including Additional Paid in Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at Dec. 31, 2011	$ 598,985	$ 1,104,144	$ (370,309)	$ 1,441	$ 1,334,261
Balance (in shares) at Dec. 31, 2011	75,834		(25,221)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		51,157			51,157
Proportionate share of other companies foreign currency translation adjustment, net of tax of $154 , $8 and $678 for 2012, 2013, and 2014 respectively				(251)	(251)
Net unrealized appreciation (depreciation) on marketable securities net of tax of $194, ($43) and ($437) for 2012, 2013 and 2014 respectively				316	316
Exercise of common stock options and issuance of restricted stock	1,879				1,879
Exercise of common stock options and issuance of restricted stock (in shares)	392
Sale of common stock under employee stock purchase plan	4,068				4,068
Sale of common stock under employee stock purchase plan (in shares)	487
Stock based compensation expense related to the issuance of stock options and restricted stock	4,693				4,693
Tax (deficiency) benefit from exercise of common stock options	138				138
Treasury stock purchases			(902)		(902)
Treasury stock purchases (in shares)			(59)
Cash dividends declared ( $0.16 per share)		(8,184)			(8,184)
Balance at Dec. 31, 2012	609,763	1,147,117	(371,211)	1,506	1,387,175
Balance (in shares) at Dec. 31, 2012	76,713		(25,280)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		58,956			58,956
Proportionate share of other companies foreign currency translation adjustment, net of tax of $154 , $8 and $678 for 2012, 2013, and 2014 respectively				66	66
Net unrealized appreciation (depreciation) on marketable securities net of tax of $194, ($43) and ($437) for 2012, 2013 and 2014 respectively				(13)	(13)
Exercise of common stock options and issuance of restricted stock	835				835
Exercise of common stock options and issuance of restricted stock (in shares)	313
Sale of common stock under employee stock purchase plan	3,696				3,696
Sale of common stock under employee stock purchase plan (in shares)	300
Stock based compensation expense related to the issuance of stock options and restricted stock	4,363				4,363
Tax (deficiency) benefit from exercise of common stock options	(146)				(146)
Treasury stock purchases			(11,739)		(11,739)
Treasury stock purchases (in shares)			(816)
Cash dividends declared ( $0.16 per share)		(8,254)			(8,254)
Balance at Dec. 31, 2013	618,511	1,197,819	(382,950)	1,559	1,434,939
Balance (in shares) at Dec. 31, 2013	77,326		(26,096)
Increase (Decrease) in Stockholders' Equity
Net Income (loss)		(24,154)			(24,154)
Proportionate share of other companies foreign currency translation adjustment, net of tax of $154 , $8 and $678 for 2012, 2013, and 2014 respectively				(1,129)	(1,129)
Net unrealized appreciation (depreciation) on marketable securities net of tax of $194, ($43) and ($437) for 2012, 2013 and 2014 respectively				(719)	(719)
Exercise of common stock options and issuance of restricted stock	287				287
Exercise of common stock options and issuance of restricted stock (in shares)	330
Sale of common stock under employee stock purchase plan	3,752				3,752
Sale of common stock under employee stock purchase plan (in shares)	295
Stock based compensation expense related to the issuance of stock options and restricted stock	5,318				5,318
Tax (deficiency) benefit from exercise of common stock options	(1,347)				(1,347)
Treasury stock purchases			(8,414)		(8,414)
Treasury stock purchases (in shares)			(669)
Cash dividends declared ( $0.16 per share)		(8,187)			(8,187)
Balance at Dec. 31, 2014	$ 626,521	$ 1,165,478	$ (391,364)	$ (289)	$ 1,400,346
Balance (in shares) at Dec. 31, 2014	77,951		(26,765)