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	54,467,000
Balance at Dec. 31, 2018	$ 545,000	$ 76,814,000	$ 498,595,000	$ 575,954,000
Net income			13,546,000	13,546,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	105,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1,000	291,000		292,000
Employee taxes paid in exchange for shares withheld		(784,000)		(784,000)
Share-based payment arrangement compensation expense		366,000		366,000
Dividends on common stock			(1,637,000)	(1,637,000)
Balance (in shares) at Mar. 31, 2019	54,572,000
Balance at Mar. 31, 2019	$ 546,000	76,687,000	510,504,000	587,737,000
Balance (in shares) at Dec. 31, 2018	54,467,000
Balance at Dec. 31, 2018	$ 545,000	76,814,000	498,595,000	575,954,000
Net income				28,736,000
Balance (in shares) at Jun. 30, 2019	54,633,000
Balance at Jun. 30, 2019	$ 546,000	77,789,000	524,055,000	602,390,000
Balance (in shares) at Mar. 31, 2019	54,572,000
Balance at Mar. 31, 2019	$ 546,000	76,687,000	510,504,000	587,737,000
Net income			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)	61,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards		466,000		$ 466,000
Share-based payment arrangement compensation expense		636,000		636,000
Dividends on common stock			(1,639,000)	(1,639,000)
Balance (in shares) at Jun. 30, 2019	54,633,000
Balance at Jun. 30, 2019	$ 546,000	77,789,000	524,055,000	602,390,000
Balance (in shares) at Dec. 31, 2019	54,703,000
Balance at Dec. 31, 2019	$ 547,000	79,465,000	517,577,000	597,589,000
Net income			13,718,000	$ 13,718,000
Repurchase and retirement of common stock (in shares)	(35,000)			(35,376)
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)	173,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 2,000	1,052,000		1,054,000
Employee taxes paid in exchange for shares withheld		(437,000)		(437,000)
Share-based payment arrangement compensation expense		246,000		246,000
Dividends on common stock			(2,193,000)	(2,193,000)
Balance (in shares) at Mar. 31, 2020	54,841,000
Balance at Mar. 31, 2020	$ 548,000	79,730,000	529,102,000	609,380,000
Balance (in shares) at Dec. 31, 2019	54,703,000
Balance at Dec. 31, 2019	$ 547,000	79,465,000	517,577,000	597,589,000
Net income				31,852,000
Balance (in shares) at Jun. 30, 2020	55,108,000
Balance at Jun. 30, 2020	$ 551,000	83,816,000	545,031,000	629,398,000
Balance (in shares) at Mar. 31, 2020	54,841,000
Balance at Mar. 31, 2020	$ 548,000	79,730,000	529,102,000	609,380,000
Net income			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)	267,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards		3,360,000		$ 3,363,000
Share-based payment arrangement compensation expense		726,000		726,000
Dividends on common stock			(2,205,000)	(2,205,000)
Balance (in shares) at Jun. 30, 2020	55,108,000
Balance at Jun. 30, 2020	$ 551,000	$ 83,816,000	$ 545,031,000	$ 629,398,000