CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Thousands, $ in Thousands	Mandatory Convertible Preferred Shares Preferred Stock	Common Shares	Capital in Excess of Par Value	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Shares	Non-controlling Interest	Total
Balance at the beginning of the period at Dec. 31, 2016		$ 334	$ 2,521,332	$ (12,119)	$ 2,033,427	$ (1,295,949)	$ 7,770	$ 3,254,795
Balance (in shares) at Dec. 31, 2016		333,598
Increase (Decrease) in Equity
Net income (loss)					(281,935)		2,888	(279,047)
Dividends to common shareholders ($0.12 per share)					(34,307)			(34,307)
Other comprehensive income (loss), net of tax				16,913			157	17,070
Issuance of common shares for stock options exercised, net of surrender of unexercised stock options		$ 1	8,299					8,300
Issuance of common shares for stock options exercised, net of surrender of unexercised stock options (in shares)		843
Share-based compensation			18,045					18,045
Equity component of exchangeable debt			116,195					116,195
Capped call transactions			(40,250)					(40,250)
Noncontrolling interest contributions (distributions), net							13,018	13,018
Other		$ 1	(7,845)				(290)	(8,134)
Other (in shares)		1,058
Balance at the end of the period at Jun. 30, 2017		$ 336	2,617,719	4,794	1,722,335	(1,295,949)	23,543	3,072,778
Balance (in shares) at Jun. 30, 2017		335,499
Increase (Decrease) in Equity
Adoption of ASU No. 2016-09 | Accounting Standards Update 2016-09			1,943		5,150			7,093
Balance at the beginning of the period at Dec. 31, 2017		$ 368	2,791,129	11,185	1,423,154	(1,314,020)	26,957	2,938,773
Balance (in shares) at Dec. 31, 2017		367,510
Increase (Decrease) in Equity
Net income (loss)					(342,953)		3,492	(339,461)
Dividends to common shareholders ($0.12 per share)					(40,511)			(40,511)
Dividends to preferred shareholders ($0.64 per share)					(3,680)			(3,680)
Common stock issuance		$ 40	301,974					302,014
Common stock issuance (in shares)		40,250
Convertible preferred stock issuance	$ 6		278,566					278,572
Convertible preferred stock issuance (in shares)	5,750,000
Other comprehensive income (loss), net of tax				(23,758)			(159)	(23,917)
Share-based compensation			14,732					14,732
Adjustment to retained earnings | Accounting Standards Update 2016-01					9,144			9,144
Adjustment to retained earnings | Accounting Standards Update 2016-16					(34,132)			(34,132)
Adjustment to retained earnings								(9,144)
Noncontrolling interest contributions (distributions), net							(4,676)	(4,676)
Less: accrued distribution on redeemable noncontrolling interest in subsidiary					(4,522)			(4,522)
Other		$ 2	(3,690)					(3,688)
Other (in shares)		2,492
Balance at the end of the period at Jun. 30, 2018	$ 6	$ 410	$ 3,382,711	$ (12,573)	$ 1,006,500	$ (1,314,020)	$ 25,614	$ 3,088,648
Balance (in shares) at Jun. 30, 2018	5,750,000	410,252