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			658,920		658,920
Stock and unit-based compensation		19,491			19,491
Stock and unit-based compensation (in shares)	1,053
Issuance of common stock in settlement of director fees		96			96
Issuance of common stock in settlement of director fees (in shares)	3
Repurchase of common stock	$ (1)	(241,282)		$ (241,283)	(241,283)
Repurchase of common stock (in shares)	(7,213)			(7,213)
Common stock dividends			(19,538)		(19,538)
Balance at Jun. 30, 2020	$ 7	1,113,412	1,365,774		2,479,193
Balance (in shares) at Jun. 30, 2020	72,358
Balance at Mar. 31, 2020	$ 8	1,341,219	1,022,902		2,364,129
Balance (in shares) at Mar. 31, 2020	79,190
Changes in stockholders' equity
Net income			352,677		352,677
Stock and unit-based compensation		9,306			9,306
Stock and unit-based compensation (in shares)	141
Issuance of common stock in settlement of directors' fees		48			48
Issuance of common stock in settlement of directors' fees (in shares)	2
Repurchase of common stock	$ (1)	(237,161)		$ (237,162)	(237,162)
Repurchase of common stock (in shares)	(6,975)			(6,975)
Common stock dividends			(9,805)		(9,805)
Balance at Jun. 30, 2020	$ 7	1,113,412	1,365,774		2,479,193
Balance (in shares) at Jun. 30, 2020	72,358
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			581,097		581,097
Stock and unit-based compensation		14,622			14,622
Stock and unit-based compensation (in shares)	803
Issuance of common stock in settlement of director fees		101			101
Issuance of common stock in settlement of director fees (in shares)	2
Repurchase of common stock	$ (1)	(443,438)		$ (443,439)	(443,439)
Repurchase of common stock (in shares)	(7,227)			(7,227)
Common stock dividends			(27,940)		(27,940)
Balance at Jun. 30, 2021	$ 6	618,337	2,895,486		3,513,829
Balance (in shares) at Jun. 30, 2021	64,484
Balance at Mar. 31, 2021	$ 7	762,585	2,704,822		3,467,414
Balance (in shares) at Mar. 31, 2021	66,961
Changes in stockholders' equity
Net income			204,229		204,229
Stock and unit-based compensation		10,621			10,621
Stock and unit-based compensation (in shares)	96
Issuance of common stock in settlement of director fees		50			50
Issuance of common stock in settlement of director fees (in shares)	1
Repurchase of common stock	$ (1)	(154,919)		$ (154,920)	(154,920)
Repurchase of common stock (in shares)	(2,574)			(2,574)
Common stock dividends			(13,565)		(13,565)
Balance at Jun. 30, 2021	$ 6	$ 618,337	$ 2,895,486		$ 3,513,829
Balance (in shares) at Jun. 30, 2021	64,484