Condensed Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock
Beginning balance at Dec. 31, 2016	$ 4,566,861	$ 0	$ 127,218	$ 490,421	$ 577,574	$ 3,890,798	$ (519,150)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	2,048,794				594,300	1,454,494
Common dividends declared	(69,494)					(69,494)
Acquisition of treasury stock	(412,989)						(412,989)
Stock-based compensation	37,034			30,190		(606)	7,450
Exercise of stock options	61,215					(38,333)	99,548
Tax Reform Reclassifications					252,400	(252,400)
Retirement of treasury stock			(3,000)	(12,135)		(178,251)	193,386
Ending balance at Dec. 31, 2017	6,231,421	0	124,218	508,476	1,424,274	4,806,208	(631,755)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	(403,333)				(1,104,799)	701,466
Common dividends declared	(71,941)					(71,941)
Acquisition of treasury stock	(421,749)						(421,749)
Stock-based compensation	39,792			28,836		(1,803)	12,759
Exercise of stock options	36,091					(24,811)	60,902
Retirement of treasury stock			(3,000)	(12,898)		(200,547)	216,445
Ending balance at Dec. 31, 2018	5,415,177	0	121,218	524,414	319,475	5,213,468	(763,398)
Increase (Decrease) in Stockholders' Equity
Comprehensive income (loss)	2,286,145				1,525,355	760,790
Common dividends declared	(75,060)					(75,060)
Acquisition of treasury stock	(459,569)						(459,569)
Stock-based compensation	44,843			25,132		(6,817)	26,528
Exercise of stock options	83,163					(51,892)	135,055
Retirement of treasury stock			(4,000)	(17,992)		(288,768)	310,760
Ending balance at Dec. 31, 2019	$ 7,294,307	$ 0	$ 117,218	$ 531,554	$ 1,844,830	$ 5,551,329	$ (750,624)