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, 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
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)
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)
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				31,852,000
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
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
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)
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
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
Repurchase and retirement of common stock (in shares)				0
Balance (in shares) at Dec. 31, 2020	82,705,000
Balance at Dec. 31, 2020	$ 827,000	85,070,000	534,436,000	$ 620,333,000
Net income	$ 0	0	18,006,000	18,006,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	70,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1,000	160,000	0	161,000
Employee taxes paid in exchange for shares withheld	0	(547,000)	0	(547,000)
Share-based payment arrangement compensation expense	0	336,000	0	336,000
Dividends on common stock	$ 0	0	(3,311,000)	(3,311,000)
Balance (in shares) at Mar. 31, 2021	82,775,000
Balance at Mar. 31, 2021	$ 828,000	85,019,000	549,131,000	634,978,000
Balance (in shares) at Dec. 31, 2020	82,705,000
Balance at Dec. 31, 2020	$ 827,000	85,070,000	534,436,000	620,333,000
Net income				$ 39,424,000
Repurchase and retirement of common stock (in shares)				0
Balance (in shares) at Jun. 30, 2021	82,881,000
Balance at Jun. 30, 2021	$ 829,000	85,578,000	567,234,000	$ 653,641,000
Balance (in shares) at Mar. 31, 2021	82,775,000
Balance at Mar. 31, 2021	$ 828,000	85,019,000	549,131,000	634,978,000
Net income	$ 0	0	21,418,000	21,418,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	106,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1,000	335,000	0	336,000
Employee taxes paid in exchange for shares withheld	0	(706,000)	0	(706,000)
Share-based payment arrangement compensation expense	0	930,000	0	930,000
Dividends on common stock	$ 0	0	(3,315,000)	(3,315,000)
Balance (in shares) at Jun. 30, 2021	82,881,000
Balance at Jun. 30, 2021	$ 829,000	$ 85,578,000	$ 567,234,000	$ 653,641,000