Condensed Consolidated Statements Of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Common Stock [Member]	Additional Paid-In Capital [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Treasury Stock [Member]	Retained Earnings [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Retained Earnings [Member]	Available-For-Sale Securities [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Available-For-Sale Securities [Member]	Foreign Currency Translation [Member] Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Foreign Currency Translation [Member]	Revision of Prior Period, Accounting Standards Update, Adjustment [Member]	Total
Balance (Accounting Standards Update 2016-02 [Member]) at Dec. 31, 2018	$ 0		$ 0		$ 0		$ (2,327)		$ 0		$ 0		$ (2,327)
Balance at Dec. 31, 2018		$ 360		$ 1,374,154		$ (2,500,556)		$ 2,573,617		$ (147)		$ (6,089)		$ 1,441,339
Balance, Shares at Dec. 31, 2018		35,973				8,276
Stock-based compensation		$ 0		19,342		$ 0		0		0		0		19,342
Stock-based compensation, Shares		0				0
Stock plan transactions and other		$ 1		(212)		$ 0		0		0		0		(211)
Stock plan transactions and other, Shares		135				0
Acquisition of treasury stock (value)		$ 0		0		$ (62,854)		0		0		0		(62,854)
Acquisition of treasury stock (shares)		0				110
Net income		$ 0		0		$ 0		88,132		0		0		88,132
Other comprehensive income (loss), net of income tax		0		0		0		0		100		278		378
Balance at Mar. 31, 2019		$ 361		1,393,284		$ (2,563,410)		2,659,422		(47)		(5,811)		1,483,799
Balance, Shares at Mar. 31, 2019		36,108				8,386
Balance (Accounting Standards Update 2016-02 [Member]) at Dec. 31, 2018	0		0		0		(2,327)		0		0		(2,327)
Balance at Dec. 31, 2018		$ 360		1,374,154		$ (2,500,556)		2,573,617		(147)		(6,089)		1,441,339
Balance, Shares at Dec. 31, 2018		35,973				8,276
Net income														277,742
Other comprehensive income (loss), net of income tax														349
Balance at Sep. 30, 2019		$ 363		1,439,811		$ (2,660,872)		2,849,032		0		(5,887)		1,622,447
Balance, Shares at Sep. 30, 2019		36,320				8,519
Balance at Mar. 31, 2019		$ 361		1,393,284		$ (2,563,410)		2,659,422		(47)		(5,811)		1,483,799
Balance, Shares at Mar. 31, 2019		36,108				8,386
Stock-based compensation		$ 0		21,322		$ 0		0		0		0		21,322
Stock-based compensation, Shares		0
Stock plan transactions and other		$ 1		(186)		0		0		0		0		(185)
Stock plan transactions and other, Shares		85
Acquisition of treasury stock (value)		$ 0		0		$ (58,512)		0		0		0		(58,512)
Acquisition of treasury stock (shares)		0				83
Net income		$ 0		0		$ 0		91,028		0		0		91,028
Other comprehensive income (loss), net of income tax		0		0		0		0		42		555		597
Balance at Jun. 30, 2019		$ 362		1,414,420		$ (2,621,922)		2,750,450		(5)		(5,256)		1,538,049
Balance, Shares at Jun. 30, 2019		36,193				8,469
Stock-based compensation		$ 0		25,506		$ 0		0		0		0		25,506
Stock plan transactions and other		$ 1		(115)		$ 0		0		0		0		(114)
Stock plan transactions and other, Shares		127				0
Acquisition of treasury stock (value)		$ 0		0		$ (38,950)		0		0		0		(38,950)
Acquisition of treasury stock (shares)		0				50
Net income		$ 0		0		$ 0		98,582		0		0		98,582
Other comprehensive income (loss), net of income tax		0		0		0		0		5		(631)		(626)
Balance at Sep. 30, 2019		$ 363		1,439,811		$ (2,660,872)		2,849,032		0		(5,887)		1,622,447
Balance, Shares at Sep. 30, 2019		36,320				8,519
Balance (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019	0		0		0		(1,051)		0		0		(1,051)
Balance at Dec. 31, 2019		$ 363		1,465,697		$ (2,699,119)		2,921,448		0		(5,363)		1,683,026
Balance, Shares at Dec. 31, 2019		36,323				8,568
Stock-based compensation		$ 0		17,708		$ 0		0		0		0		17,708
Stock-based compensation, Shares		0				0
Stock plan transactions and other		$ 2		(181)		$ 0		0		0		0		(179)
Stock plan transactions and other, Shares		194				0
Acquisition of treasury stock (value)		$ 0		0		$ (102,031)		0		0		0		(102,031)
Acquisition of treasury stock (shares)		0				134
Net income		$ 0		0		$ 0		76,388		0		0		76,388
Other comprehensive income (loss), net of income tax		0		0		0		0		0		(1,841)		(1,841)
Balance at Mar. 31, 2020		$ 365		1,483,224		$ (2,801,150)		2,996,785		0		(7,204)		1,672,020
Balance, Shares at Mar. 31, 2020		36,517				8,702
Balance (Accounting Standards Update 2016-13 [Member]) at Dec. 31, 2019	$ 0		$ 0		$ 0		$ (1,051)		$ 0		$ 0		$ (1,051)
Balance at Dec. 31, 2019		$ 363		1,465,697		$ (2,699,119)		2,921,448		0		(5,363)		1,683,026
Balance, Shares at Dec. 31, 2019		36,323				8,568
Net income														164,807
Other comprehensive income (loss), net of income tax														(81)
Balance at Sep. 30, 2020		$ 367		1,526,955		$ (2,801,496)		3,085,204		0		(5,444)		1,805,586
Balance, Shares at Sep. 30, 2020		36,682				8,703
Balance at Mar. 31, 2020		$ 365		1,483,224		$ (2,801,150)		2,996,785		0		(7,204)		1,672,020
Balance, Shares at Mar. 31, 2020		36,517				8,702
Stock-based compensation		$ 0		23,676		$ 0		0		0		0		23,676
Stock-based compensation, Shares		0
Stock plan transactions and other		$ 2		(115)		0		0		0		0		(113)
Stock plan transactions and other, Shares		150
Acquisition of treasury stock (value)		$ 0		0		$ (317)		0		0		0		(317)
Acquisition of treasury stock (shares)		0				1
Net income		$ 0		0		$ 0		8,175		0		0		8,175
Other comprehensive income (loss), net of income tax		0		0		0		0		0		1,055		1,055
Balance at Jun. 30, 2020		$ 367		1,506,785		$ (2,801,467)		3,004,960		0		(6,149)		1,704,496
Balance, Shares at Jun. 30, 2020		36,667				8,703
Stock-based compensation		$ 0		20,128		$ 0		0		0		0		20,128
Stock-based compensation, Shares		0				0
Stock plan transactions and other		$ 0		42		$ 0		0		0		0		42
Stock plan transactions and other, Shares		15				0
Acquisition of treasury stock (value)		$ 0		0		$ (29)		0		0		0		(29)
Acquisition of treasury stock (shares)		0				0
Net income		$ 0		0		$ 0		80,244		0		0		80,244
Other comprehensive income (loss), net of income tax		0		0		0		0		0		705		705
Balance at Sep. 30, 2020		$ 367		$ 1,526,955		$ (2,801,496)		$ 3,085,204		$ 0		$ (5,444)		$ 1,805,586
Balance, Shares at Sep. 30, 2020		36,682				8,703