Fair Value of Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities		$ 500,804	$ 621,231
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		270,453	397,040
Fair value of Available-for-sale securities		500,804	621,231
Fair value of other current assets		14,478	18,266
Fair value of other non-current assets		16,340	27,951
Fair value of financial assets, Total		802,075	1,064,488
Fair value of other current liabilities		105,408	56,545
Fair value of other non-current liabilities		165,566	66,423
Fair value of financial liabilities, Total		270,974	122,968
Fair Value, Measurements, Recurring | Overnight Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		261,236	290,731
Fair Value, Measurements, Recurring | Money Market Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		9,217	106,309
Fair Value, Measurements, Recurring | Nonqualified Deferred Compensation Plan Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		959	1,591
Fair value of other non-current liabilities		26,287	30,703
Fair Value, Measurements, Recurring | Forward Foreign Currency Exchange Contract, Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities	[1]	7,000	2,008
Fair value of other non-current liabilities	[1]	4,004	3,057
Fair Value, Measurements, Recurring | Contingent Acquisition Consideration Payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		97,449	52,946
Fair value of other non-current liabilities		135,275	32,663
Fair Value, Measurements, Recurring | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		5,585	56,951
Fair value of Available-for-sale securities, non-current		5,932	6,969
Fair Value, Measurements, Recurring | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		74,504	42,673
Fair value of Available-for-sale securities, non-current		247,851	315,240
Fair Value, Measurements, Recurring | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		6,247	12,733
Fair Value, Measurements, Recurring | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		100,064	83,222
Fair value of Available-for-sale securities, non-current		60,497	103,316
Fair Value, Measurements, Recurring | Greek Government-Issued Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, non-current		124	127
Fair Value, Measurements, Recurring | Nonqualified Deferred Compensation Plan Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets		170	440
Fair value of other non-current assets		7,464	6,362
Fair Value, Measurements, Recurring | Forward Foreign Current Exchange Contract Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets	[1]	6,958	10,478
Fair value of other non-current assets	[1]	734	3,533
Fair Value, Measurements, Recurring | Restrictive Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets	[2]	7,350	7,348
Fair Value, Measurements, Recurring | Strategic Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other non-current assets	[3]	8,142	18,056
Fair Value, Measurements, Recurring | Quoted Price In Active Markets For Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		261,236	290,731
Fair value of other non-current assets		8,142	18,056
Fair value of financial assets, Total		269,378	308,787
Fair value of other current liabilities		789	1,151
Fair value of other non-current liabilities		18,823	24,341
Fair value of financial liabilities, Total		19,612	25,492
Fair Value, Measurements, Recurring | Quoted Price In Active Markets For Identical Assets (Level 1) | Overnight Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		261,236	290,731
Fair Value, Measurements, Recurring | Quoted Price In Active Markets For Identical Assets (Level 1) | Nonqualified Deferred Compensation Plan Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		789	1,151
Fair value of other non-current liabilities		18,823	24,341
Fair Value, Measurements, Recurring | Quoted Price In Active Markets For Identical Assets (Level 1) | Strategic Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other non-current assets	[3]	8,142	18,056
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		9,217	106,309
Fair value of Available-for-sale securities		500,804	621,231
Fair value of other current assets		14,478	18,266
Fair value of other non-current assets		8,198	9,895
Fair value of financial assets, Total		532,697	755,701
Fair value of other current liabilities		7,170	2,448
Fair value of other non-current liabilities		11,468	9,419
Fair value of financial liabilities, Total		18,638	11,867
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Money Market Instruments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Cash and cash equivalents		9,217	106,309
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Nonqualified Deferred Compensation Plan Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		170	440
Fair value of other non-current liabilities		7,464	6,362
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Forward Foreign Currency Exchange Contract, Liability
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities	[1]	7,000	2,008
Fair value of other non-current liabilities	[1]	4,004	3,057
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		5,585	56,951
Fair value of Available-for-sale securities, non-current		5,932	6,969
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		74,504	42,673
Fair value of Available-for-sale securities, non-current		247,851	315,240
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		6,247	12,733
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, current		100,064	83,222
Fair value of Available-for-sale securities, non-current		60,497	103,316
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Greek Government-Issued Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Available-for-sale securities, non-current		124	127
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Nonqualified Deferred Compensation Plan Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets		170	440
Fair value of other non-current assets		7,464	6,362
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Forward Foreign Current Exchange Contract Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets	[1]	6,958	10,478
Fair value of other non-current assets	[1]	734	3,533
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Restrictive Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current assets	[2]	7,350	7,348
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		97,449	52,946
Fair value of other non-current liabilities		135,275	32,663
Fair value of financial liabilities, Total		232,724	85,609
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Contingent Acquisition Consideration Payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of other current liabilities		97,449	52,946
Fair value of other non-current liabilities		$ 135,275	$ 32,663

[1] See Note 12 to these Condensed Consolidated Financial Statements for further information regarding the derivative instruments.

[2] The restricted investments at March 31, 2016 and December 31, 2015 secure the Company’s irrevocable standby letter of credit obtained in connection with certain commercial agreements.

[3] The Company has investments in marketable equity securities measured using quoted prices in an active market that are considered strategic investments. See Note 7 to these Condensed Consolidated Financial Statements for additional discussion regarding the Company’s strategic investments.