CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings	Treasury Stock	Total
Balance at Dec. 31, 2017	$ 191	$ 26,890	$ 257,516	$ (18,123)	$ 266,474
Balance (in shares) at Dec. 31, 2017	17,759,446
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		85		465	550
Net exercise of stock options (in shares)	32,938
Stock-based compensation expense		566			566
Adjustment to beginning retained earnings for accounting changes in accordance with the new revenue recognition standard			(4,858)		(4,858)
Net income			6,741		6,741
Balance at Mar. 31, 2018	$ 191	27,541	259,399	(17,658)	269,473
Balance (in shares) at Mar. 31, 2018	17,792,384
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
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		241		804	$ 1,045
Net exercise of stock options (in shares)	57,670
Stock-based compensation expense		915			915
Net income			7,015		7,015
Balance at Mar. 31, 2019	$ 191	$ 31,267	$ 293,771	$ (15,072)	$ 310,157
Balance (in shares) at Mar. 31, 2019	17,976,691				17,976,691