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, 2015	$ 580,457	$ 448	$ 697,570	$ (2,543,229)	$ 2,692,317	$ (266,649)
Beginning balance, shares at Dec. 31, 2015		27,090,118
Stock Issued During Period, Value, Treasury Stock Reissued	(25,471)			(36,450)	(10,979)
Exercise of stock options and restricted stock units, shares		278,623
Repurchases of common stock	(499,992)			(499,992)
Repurchases of common stock, shares		(1,348,507)
Tax benefit resulting from exercise of certain employee stock options	17,680		17,680
Adjustment to Additional Paid in Capital, Share-Based Compensation	15,306		15,306
Net Income (Loss) Attributable to Parent	384,370				384,370
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(88,349)					(88,349)
Ending balance at Dec. 31, 2016	$ 434,943	$ 448	730,556	(3,006,771)	3,065,708	(354,998)
Ending balance, shares at Dec. 31, 2016	26,020,234	26,020,234
Stock Issued During Period, Value, Treasury Stock Reissued	$ (8,201)			(10,657)	(2,456)
Exercise of stock options and restricted stock units, shares	76,849	76,849
Repurchases of common stock	$ (124,997)			(124,997)
Repurchases of common stock, shares	(275,088)	(275,088)
Adjustment to Additional Paid in Capital, Share-Based Compensation			3,822
Income Tax Effects Allocated Directly to Equity, Cumulative Effect of Change in Accounting Principle	$ 1,539
Net Income (Loss) Attributable to Parent	92,466				92,466
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	23,878					23,878
Ending balance at Mar. 31, 2017	$ 439,852	$ 448	$ 734,378	$ (3,121,111)	$ 3,157,257	$ (331,120)
Ending balance, shares at Mar. 31, 2017	25,821,995	25,821,995