CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) shares in Thousands, $ in Thousands	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)				(148,984)		917	(148,067)
Dividends to shareholders				(17,153)			(17,153)
Other comprehensive income (loss), net of tax			783			49	832
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		10,280					10,280
Equity component of exchangeable debt		116,195					116,195
Capped call transactions		(40,250)					(40,250)
Adoption of ASU No. 2016-09 | Accounting Standards Update 2016-09		1,943		5,150			7,093
Other	$ 1	(5,342)				(290)	(5,631)
Other (in shares)	1,126
Balance at the end of the period at Mar. 31, 2017	$ 336	2,612,457	(11,336)	1,872,440	(1,295,949)	8,446	3,186,394
Balance (in shares) at Mar. 31, 2017	335,567
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)				(144,201)		539	(143,662)
Dividends to shareholders				(19,050)			(19,050)
Other comprehensive income (loss), net of tax			(18,336)			(96)	(18,432)
Share-based compensation		8,628					8,628
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)
Accrued distribution on redeemable noncontrolling interest in subsidiary				(2,399)			(2,399)
Other	$ 2	(1,864)					(1,862)
Other (in shares)	2,810
Balance at the end of the period at Mar. 31, 2018	$ 370	$ 2,797,893	$ (7,151)	$ 1,232,516	$ (1,314,020)	$ 27,400	$ 2,737,008
Balance (in shares) at Mar. 31, 2018	370,320