CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Total
Balance at Dec. 31, 2015	$ 191	$ 22,728	$ 207,404	$ (26,404)	$ 203,919
Balance (in shares) at Dec. 31, 2015	17,202,699
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		(1,312)		4,246	2,934
Net exercise of stock options (in shares)	265,570
Excess tax benefit from stock-based compensation		737			737
Stock-based compensation expense		1,681			1,681
Net income			24,574		24,574
Balance at Dec. 31, 2016	$ 191	23,834	231,978	(22,158)	233,845
Balance (in shares) at Dec. 31, 2016	17,468,269
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		812		4,035	4,847
Net exercise of stock options (in shares)	291,177
Stock-based compensation expense		2,244			2,244
Net income			25,538		25,538
Balance at Dec. 31, 2017	$ 191	26,890	257,516	(18,123)	$ 266,474
Balance (in shares) at Dec. 31, 2017	17,759,446				17,759,446
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		90		2,247	$ 2,337
Net exercise of stock options (in shares)	159,575
Stock-based compensation expense		3,131			3,131
Adjustment to beginning retained earnings for accounting changes in accordance with the new revenue recognition standard			(4,858)		(4,858)
Net income			34,098		34,098
Balance at Dec. 31, 2018	$ 191	$ 30,111	$ 286,756	$ (15,876)	$ 301,182
Balance (in shares) at Dec. 31, 2018	17,919,021				17,919,021