Consolidated Condensed Statements of Stockholders' Equity (Unaudited) - USD ($)	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2018	81,700,000
Balance at Dec. 31, 2018	$ 817,000	$ 76,814,000	$ 498,323,000	$ 575,954,000
Net income	$ 0	0	13,546,000	13,546,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	158,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 2,000	291,000	(1,000)	292,000
Employee taxes paid in exchange for shares withheld	0	(784,000)	0	(784,000)
Share-based payment arrangement compensation expense	0	366,000	0	366,000
Dividends on common stock	$ 0	0	(1,637,000)	(1,637,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	158,000
Balance (in shares) at Mar. 31, 2019	81,858,000
Balance at Mar. 31, 2019	$ 819,000	76,687,000	510,231,000	587,737,000
Balance (in shares) at Dec. 31, 2018	81,700,000
Balance at Dec. 31, 2018	$ 817,000	76,814,000	498,323,000	575,954,000
Net income				45,323,000
Balance (in shares) at Sep. 30, 2019	82,031,000
Balance at Sep. 30, 2019	$ 820,000	78,840,000	503,197,000	582,857,000
Balance (in shares) at Mar. 31, 2019	81,858,000
Balance at Mar. 31, 2019	$ 819,000	76,687,000	510,231,000	587,737,000
Net income	$ 0	0	15,190,000	$ 15,190,000
Repurchase and retirement of common stock (in shares)				0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	92,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 0	466,000	0	$ 466,000
Share-based payment arrangement compensation expense	0	636,000	0	636,000
Dividends on common stock	$ 0	0	(1,639,000)	(1,639,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	92,000
Balance (in shares) at Jun. 30, 2019	81,950,000
Balance at Jun. 30, 2019	$ 819,000	77,789,000	523,782,000	602,390,000
Net income	$ 0	0	16,587,000	$ 16,587,000
Repurchase and retirement of common stock (in shares)				0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	81,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1,000	658,000	0	$ 659,000
Share-based payment arrangement compensation expense	0	393,000	0	393,000
Dividends on common stock	$ 0	0	(37,172,000)	(37,172,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	81,000
Balance (in shares) at Sep. 30, 2019	82,031,000
Balance at Sep. 30, 2019	$ 820,000	78,840,000	503,197,000	582,857,000
Balance (in shares) at Dec. 31, 2019	82,055,000
Balance at Dec. 31, 2019	$ 821,000	79,465,000	517,303,000	597,589,000
Net income	$ 0	0	13,718,000	$ 13,718,000
Repurchase and retirement of common stock (in shares)	(53,000)			(53,064)
Repurchase and retirement of common stock	$ (1,000)	(596,000)	0	$ (597,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	259,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 3,000	1,052,000	(1,000)	1,054,000
Employee taxes paid in exchange for shares withheld	0	(437,000)	0	(437,000)
Share-based payment arrangement compensation expense	0	246,000	0	246,000
Dividends on common stock	$ 0	0	(2,193,000)	(2,193,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	259,000
Balance (in shares) at Mar. 31, 2020	82,261,000
Balance at Mar. 31, 2020	$ 823,000	79,730,000	528,827,000	609,380,000
Balance (in shares) at Dec. 31, 2019	82,055,000
Balance at Dec. 31, 2019	$ 821,000	79,465,000	517,303,000	597,589,000
Net income				49,896,000
Balance (in shares) at Sep. 30, 2020	82,681,000
Balance at Sep. 30, 2020	$ 827,000	84,389,000	559,492,000	644,708,000
Balance (in shares) at Mar. 31, 2020	82,261,000
Balance at Mar. 31, 2020	$ 823,000	79,730,000	528,827,000	609,380,000
Net income	$ 0	0	18,134,000	$ 18,134,000
Repurchase and retirement of common stock (in shares)				0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	401,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 4,000	3,360,000	(1,000)	$ 3,363,000
Share-based payment arrangement compensation expense	0	726,000	0	726,000
Dividends on common stock	$ 0	0	(2,205,000)	(2,205,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	401,000
Balance (in shares) at Jun. 30, 2020	82,662,000
Balance at Jun. 30, 2020	$ 827,000	83,816,000	544,755,000	629,398,000
Net income	$ 0	0	18,044,000	$ 18,044,000
Repurchase and retirement of common stock (in shares)				0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	19,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 0	181,000	0	$ 181,000
Share-based payment arrangement compensation expense	0	392,000	0	392,000
Dividends on common stock	$ 0	0	(3,307,000)	(3,307,000)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	19,000
Balance (in shares) at Sep. 30, 2020	82,681,000
Balance at Sep. 30, 2020	$ 827,000	$ 84,389,000	$ 559,492,000	$ 644,708,000