STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands		Total	Cumulative Effect, Period of Adoption, 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 income (loss)	Retained earnings	Retained earnings Cumulative Effect, Period of Adoption, Adjustment	[1]	Retained earnings Class A common stock	Retained earnings Class B common stock	Treasury stock		Deferred compensation
Balance, beginning of year at Dec. 31, 2017		$ 857,344	$ (38,392)				$ 1,992	$ 178	$ 16,470	$ (156,059)	$ 2,140,853	$ (38,392)				$ (1,155,668)		$ 9,578
Increase (Decrease) in Shareholders' Equity
Accounting standards update		us-gaap:AccountingStandardsUpdate201409Member
Net income		$ 288,224									288,224
Other comprehensive income		25,775								25,775
Dividends declared					$ (157,964)	$ (1,304)								$ (157,964)	$ (1,304)
Net purchase of treasury stock	[2]	(11)							(11)
Deferred compensation		0														(2,566)		2,566
Rabbi trust distribution		0														609	[3]	(609)	[3]
Balance, end of year at Dec. 31, 2018		973,672					1,992	178	16,459	(130,284)	2,231,417					(1,157,625)		11,535
Increase (Decrease) in Shareholders' Equity
Net income		316,821									316,821
Other comprehensive income		13,416								13,416
Dividends declared					(169,283)	(1,397)								(169,283)	(1,397)
Net purchase of treasury stock	[2]	24							24
Deferred compensation		0														(2,208)		2,208
Rabbi trust distribution		0														923	[3]	(923)	[3]
Balance, end of year 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		us-gaap:AccountingStandardsUpdate201613Member
Net income		$ 293,304									293,304
Other comprehensive income		38,725								38,725
Dividends declared					$ (273,902)	$ (2,261)								$ (273,902)	$ (2,261)
Net purchase of treasury stock	[2]	4							4
Deferred compensation		0														(5,465)		5,465
Rabbi trust distribution		0														705	[3]	(705)	[3]
Balance, end of year at Dec. 31, 2020		$ 1,188,048					$ 1,992	$ 178	$ 16,487	$ (78,143)	$ 2,393,624					$ (1,163,670)		$ 17,580

[1] (1) Cumulative effect adjustments in 2018 are primarily related to the implementation of new revenue recognition guidance effective January 1, 2018. The Cumulative effect adjustment in 2020 is related to the implementation of new credit loss allowance accounting guidance effective January 1, 2020. See Note 2, "Significant Accounting Policies."

[2] (2) Net purchases of treasury stock in 2018, 2019 and 2020 includes the repurchase of our Class A common stock in the open market that were subsequently distributed to satisfy stock based compensation awards. See Note 11, "Incentive and Deferred Compensation Plans".

[3] (3) Distributions of our Class A shares were made from the rabbi trust to a retired director and an incentive compensation deferral plan participant in 2018, 2019 and 2020. See Note 11, "Incentive and Deferred Compensation Plans".