Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2016	54,392
Balance at Dec. 31, 2016	$ 544	$ 74,175	$ 362,619	$ 437,338
Net income			90,284	90,284
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	141
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 1	1,089		1,090
Employee taxes paid in exchange for shares withheld		(47)		(47)
Share-based payment arrangement compensation expense		1,250		1,250
Dividends on common stock			(4,361)	(4,361)
Cash in lieu of fractional shares from stock split	$ 0	(54)	0	$ (54)
Repurchase and retirement of common stock (in shares)				0
Balance (in shares) at Dec. 31, 2017	54,533
Balance at Dec. 31, 2017	$ 545	76,413	448,542	$ 525,500
Net income			55,027	55,027
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	134
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards		936		938
Employee taxes paid in exchange for shares withheld		(104)		(104)
Share-based payment arrangement compensation expense		3,323		3,323
Dividends on common stock			(5,459)	(5,459)
Adoption of accounting standard			485	485
Repurchase and retirement of common stock (in shares)	(200)
Repurchase and retirement of common stock	$ (2)	(3,754)	0	(3,756)
Balance (in shares) at Dec. 31, 2018	54,467
Balance at Dec. 31, 2018	$ 545	76,814	498,595	575,954
Net income			61,071	61,071
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	236
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 2	1,618		1,620
Employee taxes paid in exchange for shares withheld		(784)		(784)
Share-based payment arrangement compensation expense		1,817		1,817
Dividends on common stock			(42,089)	$ (42,089)
Repurchase and retirement of common stock (in shares)				0
Balance (in shares) at Dec. 31, 2019	54,703
Balance at Dec. 31, 2019	$ 547	$ 79,465	$ 517,577	$ 597,589