Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Repurchased Stock	Additional Paid-In Capital	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2014		17,151,868	0
Beginning balance at Dec. 31, 2014	$ 234,218	$ 172	$ 0	$ 169,654	$ 64,392
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued for cash (in shares)		213,921
Stock issued for cash	55	$ 1		54
Stock issued for director compensation (in shares)		2,248
Stock issued for director compensation	66			66
Repurchased shares of common and restricted stock from stockholders (in shares)		(56,272)	(1,322,846)
Repurchased shares of common and restricted stock from stockholders	(35,310)		$ (33,526)	(1,784)
Stock-based compensation	$ 6,229			6,229
Repurchased and retired shares of common stock (in shares)	1,322,846	1,322,952	1,322,846
Repurchased and retired shares of common stock		$ (13)	$ 33,526		(33,513)
Excess tax benefit (expense) from stock based compensation	$ (519)			(519)
Net income	32,414				32,414
Ending balance at Dec. 31, 2015	237,153	$ 160	$ 0	173,700	63,293
Ending balance (in shares) at Dec. 31, 2015		15,988,813	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued for cash (in shares)		167,270
Stock issued for cash	119	$ 1		118
Stock issued for director compensation (in shares)		2,322
Stock issued for director compensation	47			47
Repurchased shares of common and restricted stock from stockholders (in shares)		(49,512)
Repurchased shares of common and restricted stock from stockholders	(848)			(848)
Stock-based compensation	$ 5,164			5,164
Repurchased and retired shares of common stock (in shares)	0
Excess tax benefit (expense) from stock based compensation	$ (1,120)			(1,120)
Net income	24,155				24,155
Ending balance at Dec. 31, 2016	264,670	$ 161	$ 0	177,061	87,448
Ending balance (in shares) at Dec. 31, 2016		16,108,893	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock issued for cash (in shares)		223,800
Stock issued for cash	98	$ 2		96
Stock issued for director compensation (in shares)		3,186
Stock issued for director compensation	72			72
Repurchased shares of common and restricted stock from stockholders (in shares)		(68,065)
Repurchased shares of common and restricted stock from stockholders	(1,587)			(1,587)
Stock-based compensation	$ 5,032			5,032
Repurchased and retired shares of common stock (in shares)	0
Net income	$ 21,121				21,121
Ending balance at Dec. 31, 2017	$ 289,406	$ 163	$ 0	$ 180,674	$ 108,569
Ending balance (in shares) at Dec. 31, 2017		16,267,814	0