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 loss, net of tax	(20,334)				(20,334)
Acquisition of common stock	(3,322)		33,000			(36,322)
Share-based compensation expense	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	433,758
Other comprehensive loss, net of tax	(14,339)
Stockholders' Equity ending balance at Jun. 30, 2019	3,843,372	123	2,427,640	4,251,414	(928,197)	(1,907,608)
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 loss, net of tax	5,995				5,995
Acquisition of common stock	(702)					(702)
Share-based compensation expense	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)
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 loss, net of tax	(619,659)				(619,659)
Acquisition of common stock	(530,237)		75,000			(605,237)
Share-based compensation expense	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	305,548
Other comprehensive loss, net of tax	(609,510)
Stockholders' Equity ending balance at Jun. 30, 2020	2,966,434	126	2,690,966	5,018,277	(1,581,975)	(3,160,960)
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 loss, net of tax	10,149				10,149
Acquisition of common stock	(32,230)					(32,230)
Share-based compensation expense	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)