Consolidated Statements of Stockholders' Equity (Unaudited) Statement - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Beginning balance, common stock, shares issued at Dec. 31, 2019		44,353
Beginning balance, net of taxes at Dec. 31, 2019	$ 701,330	$ 444	$ (138,909)	$ 533,345	$ (50,248)	$ 356,698
Beginning balance, treasury stock, shares at Dec. 31, 2019			5,367
Net income	12,200					12,200
Other comprehensive income (loss)	215				215
Common stock issued, shares		211
Common stock issued, value	2	$ 2
Stock-based compensation	1,674			1,674
Common stock dividends	$ (3,866)					(3,866)
Dividends declared per common share	$ 0.10
Tax withholding payments on stock-based awards	$ (3,309)			(3,309)
Proceeds from exercise of stock options	27			27
Other	(2)			(2)
Ending balance, common stock, shares issued at Mar. 31, 2020		44,564
Ending balance, net of taxes at Mar. 31, 2020	708,271	$ 446	$ (138,909)	531,735	(50,033)	365,032
Ending balance, treasury stock, shares at Mar. 31, 2020			5,367
Beginning balance, common stock, shares issued at Dec. 31, 2019		44,353
Beginning balance, net of taxes at Dec. 31, 2019	701,330	$ 444	$ (138,909)	533,345	(50,248)	356,698
Beginning balance, treasury stock, shares at Dec. 31, 2019			5,367
Net income	148,978
Other comprehensive income (loss)	$ 516
Dividends declared per common share	$ 1.90
Ending balance, common stock, shares issued at Sep. 30, 2020		44,568
Ending balance, net of taxes at Sep. 30, 2020	$ 778,136	$ 446	$ (138,909)	536,025	(49,732)	430,306
Ending balance, treasury stock, shares at Sep. 30, 2020			5,367
Beginning balance, common stock, shares issued at Mar. 31, 2020		44,564
Beginning balance, net of taxes at Mar. 31, 2020	708,271	$ 446	$ (138,909)	531,735	(50,033)	365,032
Beginning balance, treasury stock, shares at Mar. 31, 2020			5,367
Net income	33,586					33,586
Other comprehensive income (loss)	150				150
Stock-based compensation	1,671			1,671
Common stock dividends	$ (3,970)					(3,970)
Dividends declared per common share	$ 0.10
Ending balance, common stock, shares issued at Jun. 30, 2020		44,564
Ending balance, net of taxes at Jun. 30, 2020	$ 739,708	$ 446	$ (138,909)	533,406	(49,883)	394,648
Ending balance, treasury stock, shares at Jun. 30, 2020			5,367
Net income	103,192					103,192
Other comprehensive income (loss)	151				151
Common stock issued, shares		4
Common stock issued, value	0	$ 0
Stock-based compensation	2,494			2,494
Common stock dividends	$ (67,534)					(67,534)
Dividends declared per common share	$ 1.70
Proceeds from exercise of stock options	$ 125			125
Ending balance, common stock, shares issued at Sep. 30, 2020		44,568
Ending balance, net of taxes at Sep. 30, 2020	$ 778,136	$ 446	$ (138,909)	536,025	(49,732)	430,306
Ending balance, treasury stock, shares at Sep. 30, 2020			5,367
Beginning balance, common stock, shares issued at Dec. 31, 2020	44,568	44,568
Beginning balance, net of taxes at Dec. 31, 2020	$ 850,799	$ 446	$ (138,909)	538,006	(1,078)	452,334
Beginning balance, treasury stock, shares at Dec. 31, 2020	5,367		5,367
Net income	$ 149,156					149,156
Other comprehensive income (loss)	(4)				(4)
Common stock issued, shares		130
Common stock issued, value	1	$ 1
Stock-based compensation	2,092			2,092
Common stock dividends	$ (4,116)					(4,116)
Dividends declared per common share	$ 0.10
Tax withholding payments on stock-based awards	$ (2,729)			(2,729)
Proceeds from exercise of stock options	63			63
Other	(1)			(1)
Ending balance, common stock, shares issued at Mar. 31, 2021		44,698
Ending balance, net of taxes at Mar. 31, 2021	$ 995,261	$ 447	$ (138,909)	537,431	(1,082)	597,374
Ending balance, treasury stock, shares at Mar. 31, 2021			5,367
Beginning balance, common stock, shares issued at Dec. 31, 2020	44,568	44,568
Beginning balance, net of taxes at Dec. 31, 2020	$ 850,799	$ 446	$ (138,909)	538,006	(1,078)	452,334
Beginning balance, treasury stock, shares at Dec. 31, 2020	5,367		5,367
Net income	$ 543,411
Other comprehensive income (loss)	$ (10)
Dividends declared per common share	$ 2.30
Ending balance, common stock, shares issued at Sep. 30, 2021	44,698	44,698
Ending balance, net of taxes at Sep. 30, 2021	$ 1,305,605	$ 447	$ (138,909)	541,022	(1,088)	904,133
Ending balance, treasury stock, shares at Sep. 30, 2021	5,367		5,367
Beginning balance, common stock, shares issued at Mar. 31, 2021		44,698
Beginning balance, net of taxes at Mar. 31, 2021	$ 995,261	$ 447	$ (138,909)	537,431	(1,082)	597,374
Beginning balance, treasury stock, shares at Mar. 31, 2021			5,367
Net income	302,556					302,556
Other comprehensive income (loss)	(3)				(3)
Stock-based compensation	1,411			1,411
Common stock dividends	$ (83,514)					(83,514)
Dividends declared per common share	$ 2.10
Other	$ (1)			(1)
Ending balance, common stock, shares issued at Jun. 30, 2021		44,698
Ending balance, net of taxes at Jun. 30, 2021	1,215,710	$ 447	$ (138,909)	538,841	(1,085)	816,416
Ending balance, treasury stock, shares at Jun. 30, 2021			5,367
Net income	91,699					91,699
Other comprehensive income (loss)	(3)				(3)
Stock-based compensation	2,181			2,181
Common stock dividends	$ (3,982)					(3,982)
Dividends declared per common share	$ 0.10
Ending balance, common stock, shares issued at Sep. 30, 2021	44,698	44,698
Ending balance, net of taxes at Sep. 30, 2021	$ 1,305,605	$ 447	$ (138,909)	$ 541,022	$ (1,088)	$ 904,133
Ending balance, treasury stock, shares at Sep. 30, 2021	5,367		5,367