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, 2019	$ 3,586,184			$ 9,624	$ 1,005	$ 0	$ 44,081	$ 3,658,197			$ (126,723)
Beginning balance, shareholders' equity (Cumulative effect of adoption of ASC 326) at Dec. 31, 2019	36,943							36,943
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					339,937
Stock repurchased during period		$ (286,695)		(695)			(44,081)	(241,919)
Cash dividends		(7,345)	$ (804)						$ (7,345)	$ (804)
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)
Beginning balance, shareholders' equity at Mar. 31, 2020	3,957,520			9,275	1,005	339,958	0	3,632,894			(25,612)
Beginning balance, shareholders' equity (Cumulative effect of adoption of ASC 326) at Mar. 31, 2020	$ 0							0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	Cumulative effect of adoption of ASC 326
Net income	$ 153,786							153,786
Other comprehensive income (loss), net of tax	15,948										15,948
Issuance of preferred stock	(21)					(21)
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)
Beginning balance, shareholders' equity at Dec. 31, 2020	4,229,268			8,811	1,005	339,937	0	3,867,252			12,263
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	300,104							300,104
Other comprehensive income (loss), net of tax	(34,383)										(34,383)
Cash dividends		(8,283)	(944)						(8,283)	(944)
Preferred stock dividends declared			(9,272)							(9,272)
Ending balance, shareholders' equity at Jun. 30, 2021	4,476,490			8,811	1,005	339,937	0	4,148,857			(22,120)
Beginning balance, shareholders' equity at Mar. 31, 2021	4,321,400			8,811	1,005	339,937	0	4,005,318			(33,671)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	152,788							152,788
Other comprehensive income (loss), net of tax	11,551										11,551
Cash dividends		$ (4,141)	(472)						$ (4,141)	(472)
Preferred stock dividends declared			$ (4,636)							$ (4,636)
Ending balance, shareholders' equity at Jun. 30, 2021	$ 4,476,490			$ 8,811	$ 1,005	$ 339,937	$ 0	$ 4,148,857			$ (22,120)