Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Retained earnings	Accumulated other comprehensive income
Beginning Balance at Dec. 31, 2017	$ 227,041	$ 21	$ 218,109	$ 8,639	$ 272
Beginning Balance at Dec. 31, 2017		20,976,350
Stock-based compensation	6,567		6,567
Employee stock purchases	988		988
Employee stock purchases, shares		12,013
Restricted stock awards issued, net of forfeitures, shares		53,052
Vesting of restricted stock units, shares		6,665
Shares withheld related to net restricted stock settlement	(302)		(302)
Shares withheld related to net restricted stock settlement, shares		(2,553)
Stock options exercised	6,517		6,517
Stock options exercised, shares		276,016
Net income	25,368			25,368
Other comprehensive income	727				727
Ending Balance at Jun. 30, 2018	266,906	$ 21	231,879	34,007	999
Ending Balance at Jun. 30, 2018		21,321,543
Beginning Balance at Mar. 31, 2018	246,337	$ 21	226,635	19,397	284
Beginning Balance at Mar. 31, 2018		21,214,662
Stock-based compensation	3,186		3,186
Vesting of restricted stock units, shares		459
Stock options exercised	2,058		2,058
Stock options exercised, shares		106,422
Net income	14,610			14,610
Other comprehensive income	715				715
Ending Balance at Jun. 30, 2018	266,906	$ 21	231,879	34,007	999
Ending Balance at Jun. 30, 2018		21,321,543
Beginning Balance at Dec. 31, 2018	310,424	$ 22	249,194	60,484	724
Beginning Balance at Dec. 31, 2018		21,778,632
Stock-based compensation	5,365		5,365
Employee stock purchases	1,525		1,525
Employee stock purchases, shares		16,767
Restricted stock awards issued, net of forfeitures, shares		54,602
Vesting of restricted stock units	(67)		(67)
Vesting of restricted stock units, shares		21,376
Shares withheld related to net restricted stock settlement	(718)		(718)
Shares withheld related to net restricted stock settlement, shares		(13,023)
Stock options exercised	$ 1,878		1,878
Stock options exercised, shares	75,315	75,315
Net income	$ 15,462			15,462
Other comprehensive income	(71)				(71)
Ending Balance at Jun. 30, 2019	333,798	$ 22	257,177	75,946	653
Ending Balance at Jun. 30, 2019		21,933,669
Beginning Balance at Mar. 31, 2019	321,894	$ 22	255,226	65,786	860
Beginning Balance at Mar. 31, 2019		21,931,342
Stock-based compensation	1,779		1,779
Restricted stock awards issued, net of forfeitures, shares		(12,342)
Vesting of restricted stock units	(8)		(8)
Vesting of restricted stock units, shares		10,111
Shares withheld related to net restricted stock settlement	(63)		(63)
Shares withheld related to net restricted stock settlement, shares		(978)
Stock options exercised	243		243
Stock options exercised, shares		5,536
Net income	10,160			10,160
Other comprehensive income	(207)				(207)
Ending Balance at Jun. 30, 2019	$ 333,798	$ 22	$ 257,177	$ 75,946	$ 653
Ending Balance at Jun. 30, 2019		21,933,669