Consolidated Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2015	54,600
Balance at Dec. 31, 2015	$ 546	$ 76,468	$ 332,407	$ 409,421
Net income			16,724	16,724
Repurchase and retirement of common stock (in shares)	(759)
Repurchase and retirement of common stock	$ (8)	(7,508)	3	(7,513)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	269
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 3	2,052	(1)	2,054
Tax deficiencies from share-based payment arrangement exercises		(148)		(148)
Employee taxes paid in exchange for shares withheld		(127)		(127)
Share-based payment arrangement compensation expense		668		668
Dividends on common stock			(1,622)	(1,622)
Balance (in shares) at Jun. 30, 2016	54,110
Balance at Jun. 30, 2016	$ 541	71,405	347,511	419,457
Net income			16,740	16,740
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	282
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 3	2,361	(2)	2,362
Tax benefits from share-based payment arrangement exercises		194		194
Share-based payment arrangement compensation expense		215		215
Dividends on common stock			(1,630)	(1,630)
Balance (in shares) at Dec. 31, 2016	54,392
Balance at Dec. 31, 2016	$ 544	74,175	362,619	437,338
Net income			17,355	17,355
Repurchase and retirement of common stock				0
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	122
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1	882		883
Employee taxes paid in exchange for shares withheld		(47)		(47)
Share-based payment arrangement compensation expense		730		730
Dividends on common stock			(1,635)	(1,635)
Balance (in shares) at Jun. 30, 2017	54,514
Balance at Jun. 30, 2017	$ 545	$ 75,740	$ 378,339	$ 454,624