Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Cumulative Effect, Period of Adoption, Adjustment [Member] Common Stock [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Additional Paid-in Capital [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member] Retained Earnings [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2017					81,800,000
Balance at Dec. 31, 2017	$ 0	$ 0	$ 485	$ 485	$ 818	$ 76,413	$ 448,269	$ 525,500
Net income					$ 0	0	55,027	55,027
Repurchase and retirement of common stock (in shares)					(300,000)
Repurchase and retirement of common stock					$ (3)	(3,754)		(3,756)
Repurchase and retirement of common stock							1
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)					200,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 2	936	0	938
Employee taxes paid in exchange for shares withheld					0	(104)	0	(104)
Share-based payment arrangement compensation expense					0	3,323	0	3,323
Dividends on common stock					$ 0	0	(5,459)	(5,459)
Balance (in shares) at Dec. 31, 2018					81,700,000
Balance at Dec. 31, 2018					$ 817	76,814	498,323	575,954
Net income					$ 0	0	61,071	$ 61,071
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)					355,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 4	1,618	(2)	$ 1,620
Employee taxes paid in exchange for shares withheld					0	(784)	0	(784)
Share-based payment arrangement compensation expense					0	1,817	0	1,817
Dividends on common stock					$ 0	0	(42,089)	(42,089)
Balance (in shares) at Dec. 31, 2019					82,055,000
Balance at Dec. 31, 2019					$ 821	79,465	517,303	597,589
Net income					$ 0	0	69,500	69,500
Repurchase and retirement of common stock (in shares)					(53)
Repurchase and retirement of common stock					$ (1)	(596)	0	(597)
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards (in shares)					703,000
Issuance of common stock from share-based payment arrangement exercises and vesting of performance unit awards					$ 7	4,787	(1)	4,793
Employee taxes paid in exchange for shares withheld					0	(437)	0	(437)
Share-based payment arrangement compensation expense					0	1,851	0	1,851
Dividends on common stock					$ 0	0	(52,366)	(52,366)
Balance (in shares) at Dec. 31, 2020					82,705,000
Balance at Dec. 31, 2020					$ 827	$ 85,070	$ 534,436	$ 620,333