Condensed Consolidated Statements of Stockholders' Equity Statement - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Total Stockholders' Equity at Dec. 31, 2017	$ 2,930,250	$ 3	$ 361,231	$ (217)	$ 1,830,439	$ 738,794
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	656,774				656,774
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	44,548					44,548
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	5,885		5,885
Proceeds from Issuance of Common Stock	3,872		3,872
Total Stockholders' Equity at Mar. 31, 2018	4,488,091	3	370,988	(217)	4,013,232	104,085
Total Stockholders' Equity at Dec. 31, 2017	2,930,250	3	361,231	(217)	1,830,439	738,794
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	1,194,143
Proceeds from Issuance of Common Stock	10,858
Total Stockholders' Equity at Sep. 30, 2018	4,900,481	3	382,393	(217)	4,550,601	(32,299)
Total Stockholders' Equity at Mar. 31, 2018	4,488,091	3	370,988	(217)	4,013,232	104,085
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	268,043				268,043
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(122,795)					(122,795)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	6,205		6,205
Proceeds from Issuance of Common Stock	(598)		(598)
Total Stockholders' Equity at Jun. 30, 2018	4,638,946	3	376,595	(217)	4,281,275	(18,710)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	269,326				269,326
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(13,589)					(13,589)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	7,076		7,076
Proceeds from Issuance of Common Stock	(1,278)		(1,278)
Total Stockholders' Equity at Sep. 30, 2018	4,900,481	3	382,393	(217)	4,550,601	(32,299)
Total Stockholders' Equity at Dec. 31, 2018	4,020,331	3	394,342	(49,129)	3,722,073	(46,958)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	865,195				865,195
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(34,007)					(34,007)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	8,505		8,505
Treasury Stock Reissued at Lower than Repurchase Price	3,831			5,398	(1,567)
Total Stockholders' Equity at Mar. 31, 2019	4,863,855	3	402,847	(43,731)	4,585,701	(80,965)
Total Stockholders' Equity at Dec. 31, 2018	4,020,331	3	394,342	(49,129)	3,722,073	(46,958)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	1,205,189
Proceeds from Issuance of Common Stock	9,740
Total Stockholders' Equity at Sep. 30, 2019	5,131,192	3	396,432	(30,443)	4,917,313	(152,113)
Total Stockholders' Equity at Mar. 31, 2019	4,863,855	3	402,847	(43,731)	4,585,701	(80,965)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss) Attributable to Parent	598,810				598,810
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	31,392					31,392
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	7,818		7,818
Proceeds from Issuance of Common Stock	(64)		(64)
Total Stockholders' Equity at Jun. 30, 2019	5,486,810	3	410,601	(58,732)	5,184,511	(49,573)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Value, Acquired, Cost Method	(15,001)			(15,001)
Net Income (Loss) Attributable to Parent	(258,816)				(258,816)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(102,540)					(102,540)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	9,029		9,029
Treasury Stock Reissued at Lower than Repurchase Price	0		(24,906)	33,288	(8,382)
Proceeds from Issuance of Common Stock	1,708		1,708
Total Stockholders' Equity at Sep. 30, 2019	5,131,192	$ 3	$ 396,432	(30,443)	$ 4,917,313	$ (152,113)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury Stock, Value, Acquired, Cost Method	$ (4,999)			$ (4,999)