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]
Accounting Standards Update [Extensible List]	Cumulative effect of adoption of ASC 326
Net income	$ 353,639							353,639
Other comprehensive income (loss), net of tax	112,967										112,967
Issuance of preferred stock	339,937					339,937
Stock repurchased during period		$ (333,755)		(813)			(44,081)	(288,861)
Cash dividends		(10,869)	$ (1,206)						$ (10,869)	$ (1,206)
Preferred stock dividends declared	(9,426)							(9,426)
Ending balance, shareholders' equity at Sep. 30, 2020	4,074,414			8,811	1,005	339,937	0	3,738,417			(13,756)
Beginning 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]
Net income	142,684							142,684
Other comprehensive income (loss), net of tax	(4,092)										(4,092)
Issuance of preferred stock	0					0
Stock repurchased during period		(47,060)		(118)			0	(46,942)
Cash dividends		(3,524)	(402)						(3,524)	(402)
Preferred stock dividends declared	(4,636)							(4,636)
Ending balance, shareholders' equity at Sep. 30, 2020	4,074,414			8,811	1,005	339,937	0	3,738,417			(13,756)
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	424,177							424,177
Other comprehensive income (loss), net of tax	(44,400)										(44,400)
Cash dividends		(12,426)	(1,416)						(12,426)	(1,416)
Preferred stock dividends declared	(13,908)							(13,908)
Ending balance, shareholders' equity at Sep. 30, 2021	4,581,295			8,811	1,005	339,937	0	4,263,679			(32,137)
Beginning balance, shareholders' equity at Jun. 30, 2021	4,476,490			8,811	1,005	339,937	0	4,148,857			(22,120)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	124,073							124,073
Other comprehensive income (loss), net of tax	(10,017)										(10,017)
Cash dividends		$ (4,143)	$ (472)						$ (4,143)	$ (472)
Preferred stock dividends declared	(4,636)							(4,636)
Ending balance, shareholders' equity at Sep. 30, 2021	$ 4,581,295			$ 8,811	$ 1,005	$ 339,937	$ 0	$ 4,263,679			$ (32,137)