Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
BALANCE at Dec. 31, 2019	$ 1,111,008	$ 805	$ 112,649	$ 1,294,608	$ (14,728)	$ (282,326)
Net income	23,058	0	0	23,058	0	0
Other comprehensive income (loss)	(15,490)	0	0	0	(15,490)	0
Purchases of common stock	(8,798)	0	0	0	0	(8,798)
Dividends on common stock	(6,218)	0	0	(6,218)	0	0
Equity compensation activity	(3,930)	0	(4,360)	0	0	430
Non-cash equity compensation expense	2,406	0	2,406	0	0	0
BALANCE at Mar. 31, 2020	1,102,036	805	110,695	1,311,448	(30,218)	(290,694)
BALANCE at Dec. 31, 2019	1,111,008	805	112,649	1,294,608	(14,728)	(282,326)
Net income	108,522
Other comprehensive income (loss)	(14,001)
BALANCE at Sep. 30, 2020	1,180,137	805	114,074	1,384,474	(28,729)	(290,487)
BALANCE at Mar. 31, 2020	1,102,036	805	110,695	1,311,448	(30,218)	(290,694)
Net income	39,132	0	0	39,132	0	0
Other comprehensive income (loss)	306	0	0	0	306	0
Dividends on common stock	(6,219)	0	0	(6,219)	0	0
Equity compensation activity	(5)	0	(199)	0	0	194
Non-cash equity compensation expense	1,138	0	1,138	0	0	0
BALANCE at Jun. 30, 2020	1,136,388	805	111,634	1,344,361	(29,912)	(290,500)
Net income	46,332	0	0	46,332	0	0
Other comprehensive income (loss)	1,183	0	0	0	1,183	0
Dividends on common stock	(6,219)	0	0	(6,219)	0	0
Equity compensation activity	(6)	0	(19)	0	0	13
Non-cash equity compensation expense	2,459	0	2,459	0	0	0
BALANCE at Sep. 30, 2020	1,180,137	805	114,074	1,384,474	(28,729)	(290,487)
BALANCE at Dec. 31, 2020	1,195,040	805	116,039	1,438,916	(22,833)	(337,887)
Net income	46,492	0	0	46,492	0	0
Other comprehensive income (loss)	(265)	0	0	0	(265)	0
Purchases of common stock	(5,507)	0	0	0	0	(5,507)
Dividends on common stock	(6,792)	0	0	(6,792)	0	0
Equity compensation activity	(3,740)	0	(3,953)	0	0	213
Non-cash equity compensation expense	2,502	0	2,502	0	0	0
BALANCE at Mar. 31, 2021	1,227,730	805	114,588	1,478,616	(23,098)	(343,181)
BALANCE at Dec. 31, 2020	1,195,040	805	116,039	1,438,916	(22,833)	(337,887)
Net income	182,285
Other comprehensive income (loss)	1,241
BALANCE at Sep. 30, 2021	1,306,557	805	119,776	1,598,232	(21,592)	(390,664)
BALANCE at Mar. 31, 2021	1,227,730	805	114,588	1,478,616	(23,098)	(343,181)
Net income	72,032	0	0	72,032	0	0
Other comprehensive income (loss)	2,225	0	0	0	2,225	0
Dividends on common stock	(8,151)	0	0	(8,151)	0	0
Equity compensation activity	0	0	(266)	0	0	266
Non-cash equity compensation expense	2,747	0	2,747	0	0	0
BALANCE at Jun. 30, 2021	1,296,583	805	117,069	1,542,497	(20,873)	(342,915)
Net income	63,761	0	0	63,761	0	0
Other comprehensive income (loss)	(719)	0	0	0	(719)	0
Purchases of common stock	(47,759)	0	0	0	0	(47,759)
Dividends on common stock	(8,026)	0	0	(8,026)	0	0
Equity compensation activity	(33)	0	(43)	0	0	10
Non-cash equity compensation expense	2,750	0	2,750	0	0	0
BALANCE at Sep. 30, 2021	$ 1,306,557	$ 805	$ 119,776	$ 1,598,232	$ (21,592)	$ (390,664)