CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (USD $) In Thousands, unless otherwise specified	Total	Common Stock	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income (Loss)
Balance at Dec. 31, 2010	$ 1,420,923	$ 589,610	$ 1,139,739	$ (309,628)	$ 1,202
Balance (in shares) at Dec. 31, 2010		75,245		(21,072)
Increase (Decrease) in Stockholders' Equity
Net income (loss)	(27,335)		(27,335)
Proportionate share of other companies foreign currency translation adjustment, net of tax of $8, $154 and $180 for the year ended 2013, 2012 and 2011, respectively	(295)				(295)
Net unrealized appreciation (depreciation) on marketable securities net of tax of $43, $194 and $327 for the year ended 2013, 2012 and 2011, respectively	534				534
Exercise of common stock options and issuance of restricted stock	70	70
Exercise of common stock options and issuance of restricted stock (in shares)		289
Sale of common stock under employee stock purchase plan	4,372	4,372
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	5,365	5,365
Tax (deficiency) benefit from exercise of common stock options	(432)	(432)
Treasury stock purchases	(60,681)			(60,681)
Treasury stock purchases (in shares)				(4,149)
Cash dividends declared ($0.16 per share)	(8,260)		(8,260)
Balance at Dec. 31, 2011	1,334,261	598,985	1,104,144	(370,309)	1,441
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 $8, $154 and $180 for the year ended 2013, 2012 and 2011, respectively	(251)				(251)
Net unrealized appreciation (depreciation) on marketable securities net of tax of $43, $194 and $327 for the year ended 2013, 2012 and 2011, 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	1,387,175	609,763	1,147,117	(371,211)	1,506
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 $8, $154 and $180 for the year ended 2013, 2012 and 2011, respectively	66				66
Net unrealized appreciation (depreciation) on marketable securities net of tax of $43, $194 and $327 for the year ended 2013, 2012 and 2011, 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	$ 1,434,939	$ 618,511	$ 1,197,819	$ (382,950)	$ 1,559
Balance (in shares) at Dec. 31, 2013		77,326		(26,096)