CONSOLIDATED STATEMENTS OF STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Retained Earnings Adjustment to beginning retained earnings for accounting changes in accordance with the new revenue recognition standard	Retained Earnings	Treasury Stock	Adjustment to beginning retained earnings for accounting changes in accordance with the new revenue recognition standard	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		90			2,247		2,337
Net exercise of stock options (in shares)	159,575
Stock-based compensation expense		3,131					3,131
Net income				34,098			34,098
Balance at Dec. 31, 2018	$ 191	30,111	$ (4,858)	286,756	(15,876)	$ (4,858)	301,182
Balance (in shares) at Dec. 31, 2018	17,919,021
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		979			3,099		4,078
Net exercise of stock options (in shares)	222,362
Stock-based compensation expense		4,125					4,125
Net income				31,816			31,816
Balance at Dec. 31, 2019	$ 191	35,215		318,572	(12,777)		$ 341,201
Balance (in shares) at Dec. 31, 2019	18,141,383						18,141,383
Increase (Decrease) in Stockholders' Equity
Net exercise of stock options		(4,650)			3,905		$ (745)
Net exercise of stock options (in shares)	284,747
Stock-based compensation expense		3,855					3,855
Capital contribution		78					78
Net income				23,678			23,678
Balance at Dec. 31, 2020	$ 191	$ 34,498		$ 342,250	$ (8,872)		$ 368,067
Balance (in shares) at Dec. 31, 2020	18,426,130						18,426,130