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	5,635
Repurchase of common stock		1	(63,389)
Stock-based compensation			11,750
Other comprehensive income	$ 51			51
Net income	29,581				29,581
Payment of dividends to stockholders					(9,480)
Ending balance at Jun. 30, 2018	521,829	28	152,380	(2,088)	371,509
Beginning balance at Mar. 31, 2018		29	175,352	(2,382)	360,833
Common stock issued under employee stock plans		0	978
Repurchase of common stock		1	(30,075)
Stock-based compensation			6,125
Other comprehensive income	294			294
Net income	15,381
Payment of dividends to stockholders					(4,705)
Ending balance at Jun. 30, 2018	521,829	28	152,380	(2,088)	371,509
Beginning balance at Dec. 31, 2018	527,072	28	126,164	(1,689)	402,569
Common stock issued under employee stock plans		0	5,678
Repurchase of common stock	(7,300)	0	(7,302)
Stock-based compensation			9,903
Other comprehensive income	353			353
Net income	18,078				18,078
Payment of dividends to stockholders					(9,917)
Ending balance at Jun. 30, 2019	543,865	28	134,443	(1,336)	410,730
Beginning balance at Mar. 31, 2019		28	127,769	(1,361)	404,865
Common stock issued under employee stock plans		0	1,178
Repurchase of common stock		0	0
Stock-based compensation			5,496
Other comprehensive income	25			25
Net income	10,845
Payment of dividends to stockholders					(4,980)
Ending balance at Jun. 30, 2019	$ 543,865	$ 28	$ 134,443	$ (1,336)	$ 410,730