Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale marketable securities	$ 0	$ 149,100
Prepaid expenses and other current assets	115,463	102,551
Total	(63)	149,542
Foreign exchange derivative assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets	1,136	1,021
1.25% Notes Embedded Cash Conversion Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	(47,777)	(17,659)
1.25% Call Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	46,578	17,080
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	149,100
Total	0	149,100
Level 1 [Member] | Foreign exchange derivative assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets	0	0
Level 1 [Member] | 1.25% Notes Embedded Cash Conversion Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	0	0
Level 1 [Member] | 1.25% Call Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	0	0
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Total	1,136	1,021
Level 2 [Member] | Foreign exchange derivative assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets	1,136	1,021
Level 2 [Member] | 1.25% Notes Embedded Cash Conversion Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	0	0
Level 2 [Member] | 1.25% Call Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	0	0
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available for sale marketable securities	0	0
Total	(1,199)	(579)
Level 3 [Member] | Foreign exchange derivative assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets	0	0
Level 3 [Member] | 1.25% Notes Embedded Cash Conversion Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other liabilities	(47,777)	(17,659)
Level 3 [Member] | 1.25% Call Option [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Other assets	$ 46,578	$ 17,080