Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2015	54,600,000
Balance at Dec. 31, 2015	$ 546	$ 76,468	$ 332,407	$ 409,421
Net income			33,464	33,464
Repurchase and retirement of common stock (in shares)	(759,000)
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)	551,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 6	4,413	(3)	4,416
Tax benefits from share-based payment arrangement exercises		46		46
Employee taxes paid in exchange for shares withheld		(127)		(127)
Share-based payment arrangement compensation expense		883		883
Dividends on common stock			(3,252)	(3,252)
Balance (in shares) at Dec. 31, 2016	54,392,000
Balance at Dec. 31, 2016	$ 544	74,175	362,619	437,338
Net income			90,284	$ 90,284
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)	141,000
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		(54)		(54)
Balance (in shares) at Dec. 31, 2017	54,533,000
Balance at Dec. 31, 2017	$ 545	76,413	448,542	525,500
Net income			55,027	55,027
Repurchase and retirement of common stock (in shares)	(200,000)
Repurchase and retirement of common stock	$ (2)	(3,754)		(3,756)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)	134,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards	$ 2	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)
Balance (in shares) at Dec. 31, 2018	54,467,000
Balance at Dec. 31, 2018	$ 545	$ 76,814	498,595	575,954
Adoption of accounting standard (Note 2)			$ 485	$ 485