CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Noncontrolling Interests [Member]	Total
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of new accounting standards | ASU 2018-02 [Member]	$ 0	$ 0	$ 0	$ (1,797)	$ 0	$ 0	$ (1,797)
Beginning balance at Dec. 31, 2017	$ 6,547	802,961	(32,405)	2,646,937	$ (313,220)	3,403	3,114,223
Beginning balance (in shares) at Dec. 31, 2017	65,472				(5,783)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises	$ 0	2,111	0	0	$ 10,923	0	13,034
Stock option exercises (in shares)	0				228
Issuance of stock for equity awards	$ 0	(1,014)	0	0	$ 1,014	0	0
Issuance of stock for equity awards (in shares)	0				18
Tax withholdings on equity award vesting	$ 0	0	0	0	$ (4,814)	0	(4,814)
Tax withholdings on equity award vesting (in shares)	0				(61)
Amortization of unearned share-based compensation	$ 0	13,551	0	0	$ 0	0	13,551
Total comprehensive income, net of taxes	0	0	(7,517)	61,073	0	386	53,942
Return of investment to noncontrolling interests	0	0	0	0	0	(448)	(448)
Ending balance at Jun. 30, 2018	$ 6,547	817,609	(39,922)	2,706,213	$ (306,097)	3,341	3,187,691
Ending balance (in shares) at Jun. 30, 2018	65,472				(5,598)
Beginning balance at Mar. 31, 2018	$ 6,547	810,381	(39,480)	2,677,611	$ (316,564)	3,373	3,141,868
Beginning balance (in shares) at Mar. 31, 2018	65,472				(5,800)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises	$ 0	2,242	0	0	$ 10,501	0	12,743
Stock option exercises (in shares)	0				196
Issuance of stock for equity awards	$ 0	(1,014)	0	0	$ 1,014	0	0
Issuance of stock for equity awards (in shares)	0				18
Tax withholdings on equity award vesting	$ 0	0	0	0	$ (1,048)	0	(1,048)
Tax withholdings on equity award vesting (in shares)	0				(12)
Amortization of unearned share-based compensation	$ 0	6,000	0	0	$ 0	0	6,000
Total comprehensive income, net of taxes	0	0	(442)	28,602	0	191	28,351
Return of investment to noncontrolling interests	0	0	0	0	0	(223)	(223)
Ending balance at Jun. 30, 2018	$ 6,547	817,609	(39,922)	2,706,213	$ (306,097)	3,341	3,187,691
Ending balance (in shares) at Jun. 30, 2018	65,472				(5,598)
Beginning balance at Dec. 31, 2018	$ 6,547	823,347	(33,511)	2,723,592	$ (306,788)	3,114	3,216,301
Beginning balance (in shares) at Dec. 31, 2018	65,472				(5,608)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises	$ 0	118	0	0	$ 1,838	0	1,956
Stock option exercises (in shares)	0				34
Issuance of stock for equity awards	$ 0	(1,912)	0	0	$ 1,912	0	0
Issuance of stock for equity awards (in shares)	0				34
Tax withholdings on equity award vesting	$ 0	0	0	0	$ (2,023)	0	(2,023)
Tax withholdings on equity award vesting (in shares)	0				(30)
Amortization of unearned share-based compensation	$ 0	7,907	0	0	$ 0	0	7,907
Total comprehensive income, net of taxes	0	0	6,544	91,583	0	314	98,441
Return of investment to noncontrolling interests	0	0	0	0	0	(410)	(410)
Ending balance at Jun. 30, 2019	$ 6,547	829,460	(26,967)	2,815,175	$ (305,061)	3,018	3,322,172
Ending balance (in shares) at Jun. 30, 2019	65,472				(5,570)
Beginning balance at Mar. 31, 2019	$ 6,547	827,497	(32,971)	2,767,888	$ (306,625)	3,072	3,265,408
Beginning balance (in shares) at Mar. 31, 2019	65,472				(5,599)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises	$ 0	66	0	0	$ 474	0	540
Stock option exercises (in shares)	0				9
Issuance of stock for equity awards	$ 0	(1,110)	0	0	$ 1,110	0	0
Issuance of stock for equity awards (in shares)	0				20
Tax withholdings on equity award vesting	$ 0	0	0	0	$ (20)	0	(20)
Tax withholdings on equity award vesting (in shares)	0				0
Amortization of unearned share-based compensation	$ 0	3,007	0	0	$ 0	0	3,007
Total comprehensive income, net of taxes	0	0	6,004	47,287	0	153	53,444
Return of investment to noncontrolling interests	0	0	0	0	0	(207)	(207)
Ending balance at Jun. 30, 2019	$ 6,547	$ 829,460	$ (26,967)	$ 2,815,175	$ (305,061)	$ 3,018	$ 3,322,172
Ending balance (in shares) at Jun. 30, 2019	65,472				(5,570)