Fair Value of Financial Instruments - Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 110,017	$ 168,252
Short-term investments	149,014	96,555	[1]
Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	10,244	13,893
Short-term investments	19,184
Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	38,164	86,200
Corporate Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	100,460	86,292
US Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	19,003
Bank Deposits [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		10,253
Short-term investments	10,367	10,263
Fair Value, Measurements, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	197,582	206,901
Fair Value, Measurements, Recurring [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	38,164	86,200
Fair Value, Measurements, Recurring [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	159,418	120,701
Fair Value, Measurements, Recurring [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Total financial assets	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	10,244	13,893
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	10,244	13,893
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	38,164	86,200
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	38,164	86,200
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Fair Value, Measurements, Recurring [Member] | Commercial Paper And Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	19,184
Fair Value, Measurements, Recurring [Member] | Commercial Paper And Debt Obligations [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0
Fair Value, Measurements, Recurring [Member] | Commercial Paper And Debt Obligations [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	19,184
Fair Value, Measurements, Recurring [Member] | Commercial Paper And Debt Obligations [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	100,460	86,292
Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0	0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	100,460	86,292
Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	19,003
Fair Value, Measurements, Recurring [Member] | US Government Agencies [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0
Fair Value, Measurements, Recurring [Member] | US Government Agencies [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	19,003
Fair Value, Measurements, Recurring [Member] | US Government Agencies [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	0
Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		10,253
Short-term investments	10,367	10,263
Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		0
Short-term investments	0	0
Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		10,253
Short-term investments	10,367	10,263
Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		0
Short-term investments	0	0
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets - Forward foreign exchange contracts	160
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets - Forward foreign exchange contracts	0
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets - Forward foreign exchange contracts	160
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Prepaid Expenses and Other Current Assets [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets - Forward foreign exchange contracts	$ 0
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Accrued and Other Current Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts		595
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Accrued and Other Current Liabilities [Member] | Level I [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts		0
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Accrued and Other Current Liabilities [Member] | Level II [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts		595
Forward Foreign Exchange Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Accrued and Other Current Liabilities [Member] | Level III [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts		$ 0

[1] The Condensed Consolidated Balance Sheet as of December 31, 2015 has been derived from the audited consolidated financial statements at that date but does not include all of the information and footnotes required by generally accepted accounting principles for complete financial statements.