Interim Consolidated Statements of Shareholders' Equity and Comprehensive Income (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2014	$ 719,595	$ 448	$ 670,418	$ (2,095,656)	$ 2,357,334	$ (212,949)
Beginning balance, shares at Dec. 31, 2014		28,243,007
Stock Issued During Period, Value, Treasury Stock Reissued	29,556			47,393	(17,837)
Exercise of stock options and restricted stock units, shares		403,908
Repurchases of common stock	(494,966)			(494,966)
Repurchases of common stock, shares		(1,556,797)
Tax benefit resulting from exercise of certain employee stock options	12,929		12,929
Adjustment to Additional Paid in Capital, Share-Based Compensation	14,223		14,223
Net Income (Loss) Attributable to Parent	352,820				352,820
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(53,700)					(53,700)
Ending balance at Dec. 31, 2015	$ 580,457	$ 448	697,570	(2,543,229)	2,692,317	(266,649)
Ending balance, shares at Dec. 31, 2015	27,090,118	27,090,118
Stock Issued During Period, Value, Treasury Stock Reissued	$ 5,909			7,447	(1,538)
Exercise of stock options and restricted stock units, shares	59,321	59,321
Repurchases of common stock	$ (125,000)			(125,000)
Repurchases of common stock, shares	(390,337)	(390,337)
Tax benefit resulting from exercise of certain employee stock options	$ 5,805		5,805
Adjustment to Additional Paid in Capital, Share-Based Compensation	3,656		3,656
Net Income (Loss) Attributable to Parent	65,674				65,674
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	6,832					6,832
Ending balance at Mar. 31, 2016	$ 543,333	$ 448	$ 707,031	$ (2,660,782)	$ 2,756,453	$ (259,817)
Ending balance, shares at Mar. 31, 2016	26,759,102	26,759,102