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, 2013	$ 935,052	$ 448	$ 653,250	$ (1,721,030)	$ 2,037,420	$ (35,036)
Beginning balance, shares at Dec. 31, 2013		29,487,075
Stock Issued During Period, Value, Treasury Stock Reissued	(21,047)			(39,374)	(18,327)
Exercise of stock options and restricted stock units, shares		373,431
Repurchases of common stock	(414,000)			(414,000)
Repurchases of common stock, shares		(1,617,499)
Tax benefit resulting from exercise of certain employee stock options	3,557		3,557
Adjustment to Additional Paid in Capital, Share-Based Compensation	13,611		13,611
Net earnings	338,241				338,241
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(177,913)					(177,913)
Ending balance at Dec. 31, 2014	$ 719,595	$ 448	670,418	(2,095,656)	2,357,334	(212,949)
Ending balance, shares at Dec. 31, 2014	28,243,007	28,243,007
Stock Issued During Period, Value, Treasury Stock Reissued	$ (21,834)			(32,419)	(10,585)
Exercise of stock options and restricted stock units, shares	281,627	281,627
Repurchases of common stock	$ (371,223)			(371,223)
Repurchases of common stock, shares	(1,167,796)	(1,167,796)
Tax benefit resulting from exercise of certain employee stock options	$ 1,418		1,418
Adjustment to Additional Paid in Capital, Share-Based Compensation	10,348		10,348
Net earnings	229,469				229,469
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(25,089)					(25,089)
Ending balance at Sep. 30, 2015	$ 586,352	$ 448	$ 682,184	$ (2,434,460)	$ 2,576,218	$ (238,038)
Ending balance, shares at Sep. 30, 2015	27,356,838	27,356,838