STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands		Total	Cumulative effect adjustment	[1]	Class A common stock	Class B common stock	Common stock Class A common stock	Common stock Class B common stock	Additional paid-in-capital	Accumulated other comprehensive (loss) income	Retained earnings	Retained earnings Cumulative effect adjustment	[1]	Retained earnings Class A common stock	Retained earnings Class B common stock	Treasury stock	Deferred compensation
Beginning balance at Dec. 31, 2019		$ 1,133,253	$ (1,075)				$ 1,992	$ 178	$ 16,483	$ (116,868)	$ 2,377,558	$ (1,075)				$ (1,158,910)	$ 12,820
Increase (decrease) in shareholders' equity
Accounting standards update	[1]	Accounting Standards Update 2016-13 [Member]
Net income		$ 59,326									59,326
Other comprehensive (loss) income		(29,576)								(29,576)
Dividends declared:					$ (44,572)	$ (368)								$ (44,572)	$ (368)
Net purchase of treasury stock	[2]	4							4							0
Deferred compensation		0														(772)	772
Ending balance at Mar. 31, 2020		1,116,992					1,992	178	16,487	(146,444)	2,390,869					(1,159,682)	13,592
Beginning balance at Dec. 31, 2019		1,133,253	$ (1,075)				1,992	178	16,483	(116,868)	2,377,558	$ (1,075)				(1,158,910)	12,820
Increase (decrease) in shareholders' equity
Net income		230,519
Other comprehensive (loss) income		19,337								19,337
Ending balance at Sep. 30, 2020		1,247,217					1,992	178	16,487	(97,531)	2,472,181					(1,162,917)	16,827
Beginning balance at Mar. 31, 2020		1,116,992					1,992	178	16,487	(146,444)	2,390,869					(1,159,682)	13,592
Increase (decrease) in shareholders' equity
Net income		81,977									81,977
Other comprehensive (loss) income		40,111								40,111
Dividends declared:					(44,573)	(368)								(44,573)	(368)
Net purchase of treasury stock	[2]	0							0							0
Deferred compensation		0														(3,568)	3,568
Rabbi trust distribution	[3]	0														704	(704)
Ending balance at Jun. 30, 2020		1,194,139					1,992	178	16,487	(106,333)	2,427,905					(1,162,546)	16,456
Increase (decrease) in shareholders' equity
Net income		89,216									89,216
Other comprehensive (loss) income		8,802								8,802
Dividends declared:					(44,572)	(368)								(44,572)	(368)
Net purchase of treasury stock	[2]	0							0							0
Deferred compensation		0														(371)	371
Ending balance at Sep. 30, 2020		1,247,217					1,992	178	16,487	(97,531)	2,472,181					(1,162,917)	16,827
Beginning balance at Dec. 31, 2020		1,188,048					1,992	178	16,487	(78,143)	2,393,624					(1,163,670)	17,580
Increase (decrease) in shareholders' equity
Net income		73,566									73,566
Other comprehensive (loss) income		(5,289)								(5,289)
Dividends declared:					(47,806)	(395)								(47,806)	(395)
Net purchase of treasury stock	[4]	9							9							0
Deferred compensation		0														(846)	846
Rabbi trust distribution	[5]	0														876	(876)
Ending balance at Mar. 31, 2021		1,208,133					1,992	178	16,496	(83,432)	2,418,989					(1,163,640)	17,550
Beginning balance at Dec. 31, 2020		1,188,048					1,992	178	16,487	(78,143)	2,393,624					(1,163,670)	17,580
Increase (decrease) in shareholders' equity
Net income		242,818
Other comprehensive (loss) income		581								581
Ending balance at Sep. 30, 2021		1,286,856					1,992	178	16,496	(77,562)	2,491,842					(1,167,490)	21,400
Beginning balance at Mar. 31, 2021		1,208,133					1,992	178	16,496	(83,432)	2,418,989					(1,163,640)	17,550
Increase (decrease) in shareholders' equity
Net income		79,029									79,029
Other comprehensive (loss) income		6,139								6,139
Dividends declared:					(47,805)	(394)								(47,805)	(394)
Net purchase of treasury stock	[4]	0							0							0
Deferred compensation		0														(3,668)	3,668
Rabbi trust distribution	[5]	0														97	(97)
Ending balance at Jun. 30, 2021		1,245,102					1,992	178	16,496	(77,293)	2,449,819					(1,167,211)	21,121
Increase (decrease) in shareholders' equity
Net income		90,223									90,223
Other comprehensive (loss) income		(269)								(269)
Dividends declared:					$ (47,805)	$ (395)								$ (47,805)	$ (395)
Net purchase of treasury stock	[4]	0							0							0
Deferred compensation		0														(279)	279
Ending balance at Sep. 30, 2021		$ 1,286,856					$ 1,992	$ 178	$ 16,496	$ (77,562)	$ 2,491,842					$ (1,167,490)	$ 21,400

[1] The cumulative effect adjustment is related to the implementation of credit loss allowance accounting guidance effective January 1, 2020.

[2] Net purchases of treasury stock in 2020 include the repurchase of our Class A common stock in the open market that were subsequently distributed to satisfy stock based compensation awards.

[3] Distributions of our Class A shares were made from the rabbi trust to a retired director in 2020.

[4] Net purchases of treasury stock in 2021 include the repurchase of our Class A common stock in the open market that were subsequently distributed to satisfy stock based compensation awards.

[5] Distributions of our Class A shares were made from the rabbi trust to a retired director and an incentive compensation deferral plan participant in 2021.