CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common stock	Paid-in capital	Treasury stock	Accumulated other comprehensive income (loss)	Retained earnings	ASU 2016-01 Accumulated other comprehensive income (loss)	ASU 2016-01 Retained earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting standard update							$ (18)	$ 18
Balance, beginning of year at Dec. 31, 2017		$ 370,567	$ 1,850,582	$ 0	$ (43,783)	$ 977,160
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		786	(8,917)
Reacquisition of convertible junior subordinated debentures-equity component			0
Reissuance of treasury stock, net under share-based compensation plans			0	0
Equity compensation			20,871
Purchases of common stock				(175,059)
Other comprehensive income (loss)	$ (80,413)				(80,413)
Net income	670,097					670,097
Cash dividends						0
Balance, end of year at Dec. 31, 2018	3,581,891	371,353	1,862,536	(175,059)	(124,214)	1,647,275
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting standard update					(18)
Net common stock issued under share-based compensation plans		0	0
Reacquisition of convertible junior subordinated debentures-equity component			0
Reissuance of treasury stock, net under share-based compensation plans			(11,715)	5,989
Equity compensation			18,898
Purchases of common stock				(114,126)
Other comprehensive income (loss)	196,922				196,922
Net income	673,763					673,763
Cash dividends						(42,388)
Balance, end of year at Dec. 31, 2019	4,309,234	371,353	1,869,719	(283,196)	72,708	2,278,650
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net common stock issued under share-based compensation plans		0	0
Reacquisition of convertible junior subordinated debentures-equity component			(2,673)
Reissuance of treasury stock, net under share-based compensation plans			(18,807)	9,867
Equity compensation			13,803
Purchases of common stock				(119,997)
Other comprehensive income (loss)	144,113				144,113
Net income	446,093					446,093
Cash dividends	(82,600)					(82,647)
Balance, end of year at Dec. 31, 2020	$ 4,698,986	$ 371,353	$ 1,862,042	$ (393,326)	$ 216,821	$ 2,642,096