STATEMENT OF STOCKHOLDERS' EQUITY Statement - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Beginning balance at Dec. 31, 2017		$ 29	$ 198,384	$ (2,139)	$ 351,408
Common stock issued under employee stock plans		0	8,550
Repurchase of common stock		1	(74,377)
Stock-based compensation			16,139
Other comprehensive income	$ 63			63
Net income	47,248				47,248
Payment of dividends to stockholders					(14,172)
Ending balance at Sep. 30, 2018	531,132	28	148,696	(2,076)	384,484
Beginning balance at Jun. 30, 2018		28	152,380	(2,088)	371,509
Common stock issued under employee stock plans		0	2,915
Repurchase of common stock		0	(10,988)
Stock-based compensation			4,389
Other comprehensive income	12			12
Net income	17,667
Payment of dividends to stockholders					(4,692)
Ending balance at Sep. 30, 2018	531,132	28	148,696	(2,076)	384,484
Beginning balance at Dec. 31, 2018	527,072	28	126,164	(1,689)	402,569
Common stock issued under employee stock plans		0	9,683
Repurchase of common stock	(7,300)	0	(7,302)
Stock-based compensation			15,009
Other comprehensive income	605			605
Net income	35,177				35,177
Payment of dividends to stockholders					(14,916)
Ending balance at Sep. 30, 2019	565,328	28	143,554	(1,084)	422,830
Beginning balance at Jun. 30, 2019		28	134,443	(1,336)	410,730
Common stock issued under employee stock plans		0	4,005
Repurchase of common stock		0	0
Stock-based compensation			5,106
Other comprehensive income	252			252
Net income	17,099
Payment of dividends to stockholders					(4,999)
Ending balance at Sep. 30, 2019	$ 565,328	$ 28	$ 143,554	$ (1,084)	$ 422,830