CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income	Retained Earnings (Accumulated Deficit)
Beginning balance (in shares) at Dec. 31, 2019		114,549
Beginning balance at Dec. 31, 2019	$ 371,182	$ 120	$ 457,060	$ (62,704)	$ 261	$ (23,555)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options		67
Issuance of common stock upon exercise of options	480		480
Purchases of treasury stock (in shares)		(20)
Purchases of treasury stock	(275)			(275)
Stock-based compensation	7,988		7,988
Other comprehensive income (loss), net of tax	49				49
Net income	30,065					30,065
Ending balance (in shares) at Mar. 31, 2020		114,596
Ending balance at Mar. 31, 2020	409,489	$ 120	465,528	(62,979)	310	6,510
Beginning balance (in shares) at Dec. 31, 2019		114,549
Beginning balance at Dec. 31, 2019	$ 371,182	$ 120	457,060	(62,704)	261	(23,555)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options	1,700
Net income	$ 80,017
Ending balance (in shares) at Sep. 30, 2020		116,168
Ending balance at Sep. 30, 2020	489,680	$ 121	496,489	(63,969)	577	56,462
Beginning balance (in shares) at Mar. 31, 2020		114,596
Beginning balance at Mar. 31, 2020	409,489	$ 120	465,528	(62,979)	310	6,510
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options		1,011
Issuance of common stock upon exercise of options	7,639	$ 1	7,638
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises		(54)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(835)			(835)
Stock-based compensation	8,548		8,548
Other comprehensive income (loss), net of tax	530				530
Net income	28,327					28,327
Ending balance (in shares) at Jun. 30, 2020		115,553
Ending balance at Jun. 30, 2020	$ 453,698	$ 121	481,714	(63,814)	840	34,837
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options	600	626
Issuance of common stock upon exercise of options	$ 6,020		6,020
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises		(11)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(155)			(155)
Stock-based compensation	8,755		8,755
Other comprehensive income (loss), net of tax	(263)				(263)
Net income	21,625					21,625
Ending balance (in shares) at Sep. 30, 2020		116,168
Ending balance at Sep. 30, 2020	489,680	$ 121	496,489	(63,969)	577	56,462
Beginning balance (in shares) at Dec. 31, 2020		116,735
Beginning balance at Dec. 31, 2020	523,338	$ 122	516,140	(75,795)	415	82,456
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options		1,832
Issuance of common stock upon exercise of options	10,083	$ 2	10,081
Purchases of treasury stock (in shares)		(1,282)
Purchases of treasury stock	(33,540)			(33,540)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises		(808)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(22,520)			(22,520)
Stock-based compensation	10,142		10,142
Other comprehensive income (loss), net of tax	(166)				(166)
Net income	23,465					23,465
Ending balance (in shares) at Mar. 31, 2021		116,477
Ending balance at Mar. 31, 2021	510,802	$ 124	536,363	(131,855)	249	105,921
Beginning balance (in shares) at Dec. 31, 2020		116,735
Beginning balance at Dec. 31, 2020	$ 523,338	$ 122	516,140	(75,795)	415	82,456
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options	3,600
Purchases of treasury stock (in shares)	(4,300)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(1,200)
Net income	$ 80,459
Ending balance (in shares) at Sep. 30, 2021		115,303
Ending balance at Sep. 30, 2021	540,229	$ 126	571,377	(194,304)	115	162,915
Beginning balance (in shares) at Mar. 31, 2021		116,477
Beginning balance at Mar. 31, 2021	510,802	$ 124	536,363	(131,855)	249	105,921
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options		855
Issuance of common stock upon exercise of options	6,661	$ 1	6,660
Purchases of treasury stock (in shares)		(1,365)
Purchases of treasury stock	(29,170)			(29,170)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises		(146)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(3,238)			(3,238)
Stock-based compensation	11,131		11,131
Other comprehensive income (loss), net of tax	(34)				(34)
Net income	26,523					26,523
Ending balance (in shares) at Jun. 30, 2021		115,821
Ending balance at Jun. 30, 2021	$ 522,675	$ 125	554,154	(164,263)	215	132,444
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options	900	904
Issuance of common stock upon exercise of options	$ 6,225	$ 1	6,224
Purchases of treasury stock (in shares)		(1,220)
Purchases of treasury stock	$ (25,775)			(25,775)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	(200)	(202)
Shares purchased to satisfy cost and statutory withholding requirements for net settlement of cashless option exercises	$ (4,266)			(4,266)
Stock-based compensation	10,999		10,999
Other comprehensive income (loss), net of tax	(100)				(100)
Net income	30,471					30,471
Ending balance (in shares) at Sep. 30, 2021		115,303
Ending balance at Sep. 30, 2021	$ 540,229	$ 126	$ 571,377	$ (194,304)	$ 115	$ 162,915