Consolidated Statements Of Changes In Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Retained Earnings	Treasury stock	Accumulated Other Comprehensive Income (loss), net
Balance at beginning of period at Dec. 31, 2016	$ 1,855,473	$ 135	$ 1,400,490	$ 469,505	$ 0	$ (14,657)
Balance, shares at Dec. 31, 2016		135,240,079
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of additional shares pursuant to various stock plans, shares		271,812
Issuance of shares pursuant to various stock plans, net of forfeitures and tax withholding cancellations	1,865	$ 1	1,864
Stock-based compensation	2,660		2,660
Cash dividends declared on common stock	(67,661)			(67,661)
Reclassification of stranded tax effects to retained earnings - ASU 2018-02	0			3,597		(3,597)
Comprehensive income:
Net income	139,445			139,445
Other comprehensive income (loss), net of tax	(3,527)					(3,527)
Balance, shares at Dec. 31, 2017		135,511,891
Balance at end of period at Dec. 31, 2017	1,928,255	$ 136	1,405,014	544,886	0	(21,781)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of additional shares pursuant to various stock plans, shares		130,474
Issuance of shares pursuant to various stock plans, net of forfeitures and tax withholding cancellations	469		469
Stock-based compensation	2,877		2,877
Cash dividends declared on common stock	(71,631)			(71,631)
Comprehensive income:
Net income	189,589			189,589
Other comprehensive income (loss), net of tax	$ (11,205)					(11,205)
Repurchase of treasury stock, shares	(9,002,453)	(9,002,453)
Repurchase of treasury stock	$ (150,000)				(150,000)
Equity component of convertible notes, net of taxes	$ 15,045		15,045
Balance, shares at Dec. 31, 2018	126,639,912	126,639,912
Balance at end of period at Dec. 31, 2018	$ 1,903,211	$ 136	1,423,405	662,375	(150,000)	(32,705)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of additional shares pursuant to various stock plans, shares		59,725
Issuance of shares pursuant to various stock plans, net of forfeitures and tax withholding cancellations	12		12
Stock-based compensation	4,649		4,649
Cash dividends declared on common stock	(70,935)			(70,935)
Comprehensive income:
Net income	171,040			171,040
Other comprehensive income (loss), net of tax	$ 41,854					41,854
Repurchase of treasury stock, shares	(943,094)	(943,094)
Repurchase of treasury stock	$ (13,820)				(13,820)
Balance, shares at Dec. 31, 2019	125,756,543	125,756,543
Balance at end of period at Dec. 31, 2019	$ 2,036,011	$ 136	$ 1,428,066	762,480	$ (163,820)	$ 9,149
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of unrealized losses on equity investments to retained earnings - ASU 2016-01				$ (469)