Interim Consolidated Statements of Shareholders' Equity and Comprehensive Income (Unaudited) (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2011	$ 781,137	$ 448	$ 616,202	$ (1,225,125)	$ 1,476,550	$ (86,938)
Beginning balance, shares at Dec. 31, 2011		31,590,101
Stock Issued During Period, Value, Treasury Stock Reissued	21,927			39,873	(17,946)
Exercise of stock options and restricted stock units, shares		457,732
Repurchases of common stock	(278,672)			(278,672)
Repurchases of common stock, shares		(1,637,827)
Tax benefit resulting from exercise of certain employee stock options	9,318		9,318
Adjustment to Additional Paid in Capital, Share-Based Compensation	13,185		13,185
Net Income (Loss) Attributable to Parent	290,847				290,847
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(10,523)					(10,523)
Ending balance at Dec. 31, 2012	827,219	448	638,705	(1,463,924)	1,749,451	(97,461)
Ending balance, shares at Dec. 31, 2012	30,410,006	30,410,006
Stock Issued During Period, Value, Treasury Stock Reissued	7,069			10,769	(3,700)
Exercise of stock options and restricted stock units, shares	117,014	117,014
Repurchases of common stock	(72,300)			(72,300)
Repurchases of common stock, shares	(341,109)	(341,109)
Adjustment to Additional Paid in Capital, Share-Based Compensation	2,805		2,805
Net Income (Loss) Attributable to Parent	52,544				52,544
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(17,115)					(17,115)
Ending balance at Mar. 31, 2013	$ 800,222	$ 448	$ 641,510	$ (1,525,455)	$ 1,798,295	$ (114,576)
Ending balance, shares at Mar. 31, 2013	30,185,911	30,185,911