CONDENSED CONSOLIDATED STATEMENT OF SHAREHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Capital Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Balance, beginning of period at Dec. 31, 2019		$ 18,577	$ 138,526	$ 823,702	$ (46,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		85	(5,114)
Shares issued for employee stock purchase plan		6	658
Shares issued to directors		0	0
Equity compensation expense			7,022
Net income	$ 27,779			27,779
Other comprehensive income (loss)	(1,754)				(1,754)
Balance, end of period at Jun. 30, 2020	962,582	18,668	141,092	851,481	(48,659)
Balance, beginning of period at Mar. 31, 2020		18,662	137,235	836,961	(55,049)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		6	(38)
Shares issued for employee stock purchase plan		0	0
Shares issued to directors		0	0
Equity compensation expense			3,895
Net income	14,520			14,520
Other comprehensive income (loss)	6,390				6,390
Balance, end of period at Jun. 30, 2020	962,582	18,668	141,092	851,481	(48,659)
Balance, beginning of period at Dec. 31, 2020	1,020,755	18,677	147,961	873,692	(19,575)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		28	(2,712)
Shares issued for employee stock purchase plan		7	697
Shares issued to directors		10	(10)
Equity compensation expense			8,394
Net income	59,873			59,873
Other comprehensive income (loss)	(10,380)				(10,380)
Balance, end of period at Jun. 30, 2021	1,076,662	18,722	154,330	933,565	(29,955)
Balance, beginning of period at Mar. 31, 2021		18,712	150,004	904,910	(32,771)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued for vested restricted stock units, net of shares withheld for taxes		0	(52)
Shares issued for employee stock purchase plan		0	0
Shares issued to directors		10	(10)
Equity compensation expense			4,388
Net income	28,655			28,655
Other comprehensive income (loss)	2,816				2,816
Balance, end of period at Jun. 30, 2021	$ 1,076,662	$ 18,722	$ 154,330	$ 933,565	$ (29,955)