CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock.	Additional paid-in capital	Retained earnings	Common Stock	Total
Balance at Dec. 31, 2019	$ 8	$ 1,335,107	$ 726,392		$ 2,061,507
Balance (in shares) at Dec. 31, 2019	78,515
Changes in stockholders' equity
Net income			306,243		306,243
Stock and unit-based compensation		10,185			10,185
Stock and unit-based compensation (in shares)	912
Issuance of common stock in settlement of director fees					48
Issuance of common stock in settlement of directors' fees		48			48
Issuance of common stock in settlement of directors' fees (in shares)	1
Repurchase of common stock		(4,121)		$ (4,121)	(4,121)
Repurchase of common stock (in shares)	(238)			(238)
Common stock dividends			(9,733)		(9,733)
Balance at Mar. 31, 2020	$ 8	1,341,219	1,022,902		2,364,129
Balance (in shares) at Mar. 31, 2020	79,190
Balance at Dec. 31, 2020	$ 7	1,047,052	2,342,329		3,389,388
Balance (in shares) at Dec. 31, 2020	70,906
Changes in stockholders' equity
Net income			376,868		376,868
Stock and unit-based compensation		4,001			4,001
Stock and unit-based compensation (in shares)	707
Issuance of common stock in settlement of director fees		51			51
Issuance of common stock in settlement of director fees (in shares)	1
Repurchase of common stock		(288,519)		$ (288,519)	(288,519)
Repurchase of common stock (in shares)	(4,653)			(4,653)
Common stock dividends			(14,375)		(14,375)
Balance at Mar. 31, 2021	$ 7	$ 762,585	$ 2,704,822		$ 3,467,414
Balance (in shares) at Mar. 31, 2021	66,961