Condensed Consolidated Statements of Changes in Common Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Balance, beginning of period at Dec. 31, 2023		$ 173	$ (945,870)	$ 1,430,594	$ 4,243,759	$ (330,851)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under incentive and benefit plans		0		1,531
Shares repurchased under share repurchase program (Note 14)		(2)		(50,501)
Repurchases of common stock under incentive plans			(332)
Share-based compensation				8,812
Net income	$ 152,354				152,354
Dividends and dividend equivalents declared					(38,290)
Net unrealized gains (losses) on investments, net of tax	(31,577)					(31,577)
Other adjustments to other comprehensive income (loss)						(68)
Balance, end of period at Mar. 31, 2024	4,439,732	171	(946,202)	1,390,436	4,357,823	(362,496)
Balance, beginning of period at Dec. 31, 2024	4,623,858	168	(968,246)	1,246,826	4,695,348	(350,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under incentive and benefit plans		0		1,170
Shares repurchased under share repurchase program (Note 14)		(6)		(209,144)
Repurchases of common stock under incentive plans			(1,150)
Share-based compensation				9,886
Net income	144,558				144,558
Dividends and dividend equivalents declared					(37,868)
Net unrealized gains (losses) on investments, net of tax	55,477					55,477
Other adjustments to other comprehensive income (loss)						45
Balance, end of period at Mar. 31, 2025	$ 4,586,826	$ 162	$ (969,396)	$ 1,048,738	$ 4,802,038	$ (294,716)