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
Repurchase and retirement of common stock (in shares)				0
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
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			47,525,000	47,525,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	131,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards		1,327,000		1,328,000
Share-based payment arrangement compensation expense		1,451,000		1,451,000
Dividends on common stock			(40,452,000)	(40,452,000)
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
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)
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)
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