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, 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	111,359							111,359
Other comprehensive income (loss), net of tax	28,327										28,327
Stock repurchased during period	(100,700)	$ (100,756)		(243)			(100,513)
Cash dividends		(4,173)	$ (402)						$ (4,173)	$ (402)
Ending balance, shareholders' equity at Mar. 31, 2019	3,523,309			10,380	1,005	0	393,449	3,325,335			(206,860)
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	57,169							57,169
Other comprehensive income (loss), net of tax	$ 101,111										101,111
Issuance of preferred stock	339,958					3	339,955
Stock repurchased during period	$ (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	$ 3	$ 339,955	$ 3,632,894			$ (25,612)