Consolidated Statement of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Beginning balance at Dec. 31, 2014					$ 555,767
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 82,833
Other comprehensive income	(207,348)				(207,348)
Ending balance at Jun. 30, 2015					348,419
Beginning balance at Mar. 31, 2015					548,997
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	32,789
Other comprehensive income	(200,578)				(200,578)
Ending balance at Jun. 30, 2015					348,419
Beginning balance at Dec. 31, 2015	4,523,967	$ 1,497	$ 3,148,409	$ 4,856,674	118,549	$ (3,601,162)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock plan exercises	(19,062)	5	(19,067)
Stock plan compensation	13,650		13,650
Change in tax benefit from share-based payment arrangements	7,919		7,919
Dividends	(64,966)			(64,966)
Acquisition of common stock	(451,809)					(451,809)
Net income	389,667			389,667
Other comprehensive income	208,705				208,705
Ending balance at Jun. 30, 2016	4,608,071	1,502	3,150,911	5,181,375	327,254	(4,052,971)
Beginning balance at Mar. 31, 2016					225,240
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	169,349
Other comprehensive income	102,014				102,014
Ending balance at Jun. 30, 2016	$ 4,608,071	$ 1,502	$ 3,150,911	$ 5,181,375	$ 327,254	$ (4,052,971)