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)
Comprehensive income	7,568	0	0	23,058	(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)
Comprehensive income	47,006
BALANCE at Jun. 30, 2020	1,136,388	805	111,634	1,344,361	(29,912)	(290,500)
BALANCE at Mar. 31, 2020	1,102,036	805	110,695	1,311,448	(30,218)	(290,694)
Comprehensive income	39,438	0	0	39,132	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)
BALANCE at Dec. 31, 2020	1,195,040	805	116,039	1,438,916	(22,833)	(337,887)
Comprehensive income	46,227	0	0	46,492	(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)
Comprehensive income	120,484
BALANCE at Jun. 30, 2021	1,296,583	805	117,069	1,542,497	(20,873)	(342,915)
BALANCE at Mar. 31, 2021	1,227,730	805	114,588	1,478,616	(23,098)	(343,181)
Comprehensive income	74,257	0		72,032	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)