Unaudited Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Stockholders' Equity beginning balance at Dec. 31, 2018	$ 3,340,180	$ 123	$ 2,306,843	$ 3,817,656	$ (913,858)	$ (1,870,584)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	172,107			172,107
Other comprehensive gain (loss), net of tax	(20,334)				(20,334)
Acquisition of common stock	(3,322)		33,000			(36,322)
Share-based compensation	12,541		12,541
Issuance of common stock	29,795		29,795
Stockholders' Equity ending balance at Mar. 31, 2019	3,530,967	123	2,382,179	3,989,763	(934,192)	(1,906,906)
Stockholders' Equity beginning balance at Dec. 31, 2018	3,340,180	123	2,306,843	3,817,656	(913,858)	(1,870,584)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	659,563
Other comprehensive gain (loss), net of tax	(200,820)
Stockholders' Equity ending balance at Sep. 30, 2019	3,900,310	123	2,503,590	4,477,219	(1,114,678)	(1,965,944)
Stockholders' Equity beginning balance at Mar. 31, 2019	3,530,967	123	2,382,179	3,989,763	(934,192)	(1,906,906)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	261,651			261,651
Other comprehensive gain (loss), net of tax	5,995				5,995
Acquisition of common stock	(702)					(702)
Share-based compensation	18,306		18,306
Issuance of common stock	27,155		27,155
Stockholders' Equity ending balance at Jun. 30, 2019	3,843,372	123	2,427,640	4,251,414	(928,197)	(1,907,608)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	225,805			225,805
Other comprehensive gain (loss), net of tax	(186,481)				(186,481)
Acquisition of common stock	(58,336)					(58,336)
Share-based compensation	15,273		15,273
Issuance of common stock	60,677		60,677
Stockholders' Equity ending balance at Sep. 30, 2019	3,900,310	123	2,503,590	4,477,219	(1,114,678)	(1,965,944)
Stockholders' Equity beginning balance at Dec. 31, 2019	3,711,616	124	2,494,721	4,712,729	(972,465)	(2,523,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	147,060			147,060
Other comprehensive gain (loss), net of tax	(619,659)				(619,659)
Acquisition of common stock	(530,237)		75,000			(605,237)
Share-based compensation	14,175		14,175
Issuance of common stock	73,274	1	73,273
Stockholders' Equity ending balance at Mar. 31, 2020	2,796,229	125	2,657,169	4,859,789	(1,592,124)	(3,128,730)
Stockholders' Equity beginning balance at Dec. 31, 2019	3,711,616	124	2,494,721	4,712,729	(972,465)	(2,523,493)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	494,365
Other comprehensive gain (loss), net of tax	(610,671)
Stockholders' Equity ending balance at Sep. 30, 2020	2,937,750	126	2,713,022	5,207,094	(1,583,136)	(3,399,356)
Stockholders' Equity beginning balance at Mar. 31, 2020	2,796,229	125	2,657,169	4,859,789	(1,592,124)	(3,128,730)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	158,488			158,488
Other comprehensive gain (loss), net of tax	10,149				10,149
Acquisition of common stock	(32,230)					(32,230)
Share-based compensation	8,989		8,989
Issuance of common stock	24,809	1	24,808
Stockholders' Equity ending balance at Jun. 30, 2020	2,966,434	126	2,690,966	5,018,277	(1,581,975)	(3,160,960)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	188,817			188,817
Other comprehensive gain (loss), net of tax	(1,161)				(1,161)
Acquisition of common stock	(238,396)					(238,396)
Share-based compensation	11,905		11,905
Issuance of common stock	10,151		10,151
Stockholders' Equity ending balance at Sep. 30, 2020	$ 2,937,750	$ 126	$ 2,713,022	$ 5,207,094	$ (1,583,136)	$ (3,399,356)