Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Ordinary Shares	Non-voting Euro Deferred	Capital Redemption Reserve	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Cumulative effect adjustment from adoption of new accounting standards	$ 107,687				$ 0		$ 107,687
Beginning balance (in shares) at Dec. 31, 2015		61,305	4,000
Beginning balance at Dec. 31, 2015	1,598,646	$ 6	$ 55	$ 471	1,562,900	$ (267,472)	302,686
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Issuance of ordinary shares in conjunction with exercise of share options (in shares)		399
Issuance of ordinary shares in conjunction with exercise of share options	16,880				16,880
Issuance of ordinary shares under employee stock purchase plan (in shares)		70
Issuance of ordinary shares under employee stock purchase plan	7,294				7,294
Issuance of ordinary shares in conjunction with vesting of restricted stock units (in shares)		289
Shares withheld for payment of employee's withholding tax liability	(21,234)				(21,234)
Share-based compensation	99,392				99,392
Shares repurchased (in shares)		(2,243)
Shares repurchased	(278,296)			1			(278,297)
Other comprehensive loss	(49,861)					(49,861)
Net income	396,831						396,831
Ending balance (in shares) at Dec. 31, 2016		59,820	4,000
Ending balance at Dec. 31, 2016	1,877,339	$ 6	$ 55	472	1,665,232	(317,333)	528,907
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Issuance of Exchangeable Senior Notes	149,767				149,767
Issuance of ordinary shares in conjunction with exercise of share options (in shares)		428
Issuance of ordinary shares in conjunction with exercise of share options	22,683				22,683
Issuance of ordinary shares under employee stock purchase plan (in shares)		104
Issuance of ordinary shares under employee stock purchase plan	9,141				9,141
Issuance of ordinary shares in conjunction with vesting of restricted stock units (in shares)		250
Shares withheld for payment of employee's withholding tax liability	(18,589)				(18,589)
Share-based compensation	107,252				107,252
Shares repurchased (in shares)		(704)
Shares repurchased	(98,799)						(98,799)
Other comprehensive loss	176,455					176,455
Net income	487,848						487,848
Ending balance (in shares) at Dec. 31, 2017		59,898	4,000
Ending balance at Dec. 31, 2017	2,713,097	$ 6	$ 55	472	1,935,486	(140,878)	917,956
Increase (Decrease) in Shareholders' Equity [Roll Forward]
Cumulative effect adjustment from adoption of new accounting standards	(279)					53	(332)
Issuance of ordinary shares in conjunction with exercise of share options (in shares)		772
Issuance of ordinary shares in conjunction with exercise of share options	82,918				82,918
Issuance of ordinary shares under employee stock purchase plan (in shares)		111
Issuance of ordinary shares under employee stock purchase plan	10,419				10,419
Issuance of ordinary shares in conjunction with vesting of restricted stock units (in shares)		253
Shares withheld for payment of employee's withholding tax liability	(17,925)				(17,925)
Share-based compensation	102,732				102,732
Shares repurchased (in shares)		(3,530)
Shares repurchased	(523,672)						(523,672)
Other comprehensive loss	(56,966)					(56,966)
Net income	447,098						447,098
Ending balance (in shares) at Dec. 31, 2018		57,504	4,000
Ending balance at Dec. 31, 2018	$ 2,757,422	$ 6	$ 55	$ 472	$ 2,113,630	$ (197,791)	$ 841,050