Consolidated Statements of Changes In Shareholders' Equity - USD ($) shares in Thousands, $ 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	$ 57,169							57,169
Other comprehensive income (loss), net of tax	$ 101,111										101,111
Issuance of preferred stock	339,958					339,958
Stock repurchased during period	$ (159,700)	$ (159,704)		(349)			(44,081)	(115,274)
Cash dividends		(3,739)	$ (402)						$ (3,739)	$ (402)
Ending 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 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	147,316							147,316
Other comprehensive income (loss), net of tax	(45,934)										(45,934)
Cash dividends		$ (4,142)	(472)						$ (4,142)	(472)
Preferred stock dividends declared			$ (4,636)							$ (4,636)
Ending balance, shareholders' equity at Mar. 31, 2021	$ 4,321,400			$ 8,811	$ 1,005	$ 339,937	$ 0	$ 4,005,318			$ (33,671)