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, 2018		$ 28	$ 126,164	$ (1,689)	$ 402,569
Common stock issued under employee stock plans		0	9,683
Repurchase of common stock		0	(7,302)
Stock-based compensation			15,009
Other comprehensive income (loss)	$ 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 (loss)	252			252
Net income	17,099				17,099
Payment of dividends to stockholders					(4,999)
Ending balance at Sep. 30, 2019	565,328	28	143,554	(1,084)	422,830
Beginning balance at Dec. 31, 2019	724,546	28	152,117	(3,130)	575,531
Common stock issued under employee stock plans		0	9,662
Repurchase of common stock	(2,600)	0	(2,636)
Stock-based compensation			22,049
Other comprehensive income (loss)	775			775
Net income	43,898				43,898
Payment of dividends to stockholders					(18,497)
Ending balance at Sep. 30, 2020	779,797	28	181,192	(2,355)	600,932
Beginning balance at Jun. 30, 2020		28	168,470	(1,720)	592,694
Common stock issued under employee stock plans		0	3,364
Repurchase of common stock		0	0
Stock-based compensation			9,358
Other comprehensive income (loss)	(635)			(635)
Net income	14,820				14,820
Payment of dividends to stockholders					(6,582)
Ending balance at Sep. 30, 2020	$ 779,797	$ 28	$ 181,192	$ (2,355)	$ 600,932