CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance at Dec. 31, 2020	$ 1,262,202	$ 352	$ 807,739	$ 487,912	$ (33,801)
Beginning Balance, shares (in shares) at Dec. 31, 2020		175,790
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	63,292	$ 3	63,289
Issuance of common stock under stock option plans, shares		1,703
Repurchase of common stock	(161,652)	$ (4)		(161,648)
Repurchase of common stock, shares		(2,012)
Stock-based compensation expense	43,774		43,774
Payment of dividends ($0.286 per common share)	(43,263)			(43,263)
Net income	279,881			279,881
Net unrealized gain (loss), net of tax of $4,389, $(5,943), and $(2,206) in 2023, 2022, and 2021, respectively	(7,152)				(7,152)
Net unrealized gain (loss) on available-for-sale investments, net of tax	(7,152)
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	(236)				(236)
Foreign currency translation adjustments, net of tax	(6,753)				(6,753)
Balance at Dec. 31, 2021	1,430,093	$ 351	914,802	562,882	(47,942)
Balance, shares (in shares) at Dec. 31, 2021		175,481
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	9,861	$ 1	9,860
Issuance of common stock under stock option plans, shares		514
Repurchase of common stock	(204,314)	$ (7)		(204,307)
Repurchase of common stock, shares		(3,364)
Stock-based compensation expense	54,505		54,505
Payment of dividends ($0.286 per common share)	(45,921)			(45,921)
Net income	215,525			215,525
Net unrealized gain (loss), net of tax of $4,389, $(5,943), and $(2,206) in 2023, 2022, and 2021, respectively	(17,152)				(17,152)
Net unrealized gain (loss) on available-for-sale investments, net of tax	(17,152)
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	182				182
Foreign currency translation adjustments, net of tax	(4,385)				(4,385)
Balance at Dec. 31, 2022	$ 1,438,394	$ 345	979,167	528,179	(69,297)
Balance, shares (in shares) at Dec. 31, 2022	172,631	172,631
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under stock option plans	$ 3,268	$ 1	3,267
Issuance of common stock under stock option plans, shares	330	691
Repurchase of common stock	$ (79,794)	$ (3)		(79,791)
Repurchase of common stock, shares		(1,723)
Stock-based compensation expense	54,768		54,768
Payment of dividends ($0.286 per common share)	(49,079)			(49,079)
Net income	113,234			113,234
Net unrealized gain (loss), net of tax of $4,389, $(5,943), and $(2,206) in 2023, 2022, and 2021, respectively					10,507
Net unrealized gain (loss) on available-for-sale investments, net of tax	10,507
Reclassification of net realized (gain) loss on the sale of available-for-sale investments	1,954				1,954
Foreign currency translation adjustments, net of tax	11,500				11,500
Balance at Dec. 31, 2023	$ 1,504,752	$ 343	$ 1,037,202	$ 512,543	$ (45,336)
Balance, shares (in shares) at Dec. 31, 2023	171,599	171,599