Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Treasury Stock.	Retained Earnings	Redeemable Noncontrolling Interest	Total
Changes in Total Equity
Impact of change in accounting policy (Note 2) | Adjustments for New Accounting Pronouncement | ASU 2014-09					$ (4,445)		$ (4,445)
Adjusted balance as of January 1, 2018	$ 20,277	$ 162,806	$ (36,148)	$ (909,960)	2,999,573		2,236,548
Balance (Previously reported) at Dec. 31, 2017						$ 115,689
Balance at Dec. 31, 2017						115,689
Changes in Redeemable Noncontrolling Interests
Net income						1,261
Adjustments to redemption value of redeemable noncontrolling interest						12,828
Subsidiary repurchase of noncontrolling interests						(3,778)
Balance (Previously reported) at Dec. 31, 2017	$ 20,277	162,806	(36,148)	(909,960)	3,004,018		$ 2,240,993
Balance (in shares) (Previously reported) at Dec. 31, 2017	202,765
Balance (in shares) at Dec. 31, 2017	202,765						202,765,000
Changes in Total Equity
Net income					284,276		$ 284,276
Other comprehensive loss			(8,874)				(8,874)
Common stock issued from treasury shares for exercise of stock options		6,309		22,975			29,284
Common stock unissued due to forfeiture of nonvested awards		629		(629)
Common stock issued from treasury shares for nonvested awards		(12,945)		12,945
Common stock issued from treasury for dividend equivalents		925		9			934
Share-based compensation		20,241					20,241
Cash dividends declared ($0.13 per share)					(47,803)		(47,803)
Purchase of treasury shares				(82)			(82)
Adjustments to redemption value of redeemable noncontrolling interest		(12,828)					(12,828)
Subsidiary repurchase of noncontrolling interests						$ (126,000)
Balance at Jun. 30, 2018	$ 20,277	$ 165,137	$ (45,022)	$ (874,742)	$ 3,236,046		$ 2,501,696
Balance (in shares) at Jun. 30, 2018	202,765						202,765,000