Consolidated Statements of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Class A Common Stock	Class B Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Preferred Stock	Surplus	Retained Earnings	Retained Earnings Class A Common Stock	Retained Earnings Class B Common Stock	Accumulated Other Comprehensive (Loss) Income
Beginning balance, shareholders' equity at Dec. 31, 2018	$ 3,488,954			$ 10,623	$ 1,005	$ 0	$ 493,962	$ 3,218,551			$ (235,187)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	230,718							230,718
Other comprehensive income (loss), net of tax	54,456										54,456
Stock repurchased during period	(190,500)	$ (190,530)		(448)			(190,082)
Cash dividends		(8,181)	$ (804)						$ (8,181)	$ (804)
Preferred stock dividends declared			(4,790)							(4,790)
Ending balance, shareholders' equity at Jun. 30, 2019	$ 3,574,613			$ 10,175	1,005	0	303,880	3,440,284			(180,731)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock repurchased during period (in shares)	448,500			448,500
Cash dividends (in dollars per share)	$ 0.80
Beginning balance, shareholders' equity at Mar. 31, 2019	$ 3,523,309			$ 10,380	1,005	0	393,449	3,325,335			(206,860)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	119,359							119,359
Other comprehensive income (loss), net of tax	26,129										26,129
Stock repurchased during period	(89,800)	(89,774)		(205)			(89,569)
Cash dividends		(4,008)	(402)						(4,008)	(402)
Ending balance, shareholders' equity at Jun. 30, 2019	$ 3,574,613			$ 10,175	1,005	0	303,880	3,440,284			(180,731)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock repurchased during period (in shares)	205,500			205,500
Cash dividends (in dollars per share)	$ 0.40
Beginning balance, shareholders' equity at Dec. 31, 2019	$ 3,586,184			$ 9,624	1,005	$ 0	$ 44,081	3,658,197			(126,723)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	210,955							210,955
Other comprehensive income (loss), net of tax	$ 117,059										117,059
Issuance of preferred stock	339,937,000					339,937,000	0
Stock repurchased during period	$ (286,695)			(695)			$ (44,081)	(241,919)
Cash dividends		(7,345)	(804)						(7,345)	(804)
Ending balance, shareholders' equity at Jun. 30, 2020	$ 3,991,444			$ 8,929	1,005	$ 339,937	0	3,651,237			(9,664)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock repurchased during period (in shares)	695,390			695,390
Cash dividends (in dollars per share)	$ 0.80
Beginning balance, shareholders' equity at Mar. 31, 2020	$ 3,957,520			$ 9,275	1,005	$ 339,958	$ 0	3,632,894			(25,612)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	153,786							153,786
Other comprehensive income (loss), net of tax	$ 15,948										15,948
Issuance of preferred stock	(21,000)					(21,000)	0
Stock repurchased during period	$ (126,991)			(346)			$ 0	(126,645)
Cash dividends		$ (3,606)	(402)						$ (3,606)	(402)
Preferred stock dividends declared			$ (4,790)							$ (4,790)
Ending balance, shareholders' equity at Jun. 30, 2020	$ 3,991,444			$ 8,929	$ 1,005	$ 339,937	$ 0	$ 3,651,237			$ (9,664)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock repurchased during period (in shares)	346,000			346,000
Cash dividends (in dollars per share)	$ 0.40