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		(131)	0	0	$ 422	0	291
Stock option exercises (in shares)					32
Tax withholdings on restricted stock and RSU vestings		0	0	0	$ (3,766)	0	(3,766)
Tax withholdings on restricted stock and RSU vestings (in shares)					(49)
Amortization of unearned share-based compensation	$ 0	7,551	0	0	$ 0	0	7,551
Total comprehensive income, net of taxes	0	0	(7,075)	32,471	0	195	25,591
Return of investment to noncontrolling interests	0	0	0	0	0	(225)	(225)
Ending balance at Mar. 31, 2018	$ 6,547	810,381	(39,480)	2,677,611	$ (316,564)	3,373	3,141,868
Ending balance (in shares) at Mar. 31, 2018	65,472				(5,800)
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		52	0	0	$ 1,364	0	1,416
Stock option exercises (in shares)					25
Issuance of stock for RSU vestings net of restricted stock forfeitures		(802)	0	0	$ 802	0	0
Issuance of stock for RSU vestings net of restricted stock forfeitures (in shares)					14
Tax withholdings on restricted stock and RSU vestings		0	0	0	$ (2,003)	0	(2,003)
Tax withholdings on restricted stock and RSU vestings (in shares)					(30)
Amortization of unearned share-based compensation	$ 0	4,900	0	0	$ 0	0	4,900
Total comprehensive income, net of taxes	0	0	540	44,296	0	161	44,997
Return of investment to noncontrolling interests	0	0	0	0	0	(203)	(203)
Ending balance at Mar. 31, 2019	$ 6,547	$ 827,497	$ (32,971)	$ 2,767,888	$ (306,625)	$ 3,072	$ 3,265,408
Ending balance (in shares) at Mar. 31, 2019	65,472				(5,599)