Fair Value of Financial Instruments - Assets and Liabilities Subject to Fair Value Measurements on Recurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	$ 68,096	$ 76,704
Short-term investments	41,624	38,381
Bank Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,877	10,165
Short-term investments	10,270	10,153
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	18,339	21,947
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,596	2,619
Corporate Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	31,354	28,228
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total financial assets	83,436	73,112
Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,877	10,165
Short-term investments	10,270	10,153
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	18,339	21,947
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,596	2,619
Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	31,354	28,228
Fair Value, Measurements, Recurring [Member] | Forward Foreign Exchange Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts	1,002
Level I [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total financial assets	11,596	2,619
Level I [Member] | Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Level I [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Level I [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,596	2,619
Level I [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Level I [Member] | Fair Value, Measurements, Recurring [Member] | Forward Foreign Exchange Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts	0
Level II [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total financial assets	71,840	70,493
Level II [Member] | Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	11,877	10,165
Short-term investments	10,270	10,153
Level II [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	18,339	21,947
Level II [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Level II [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	31,354	28,228
Level II [Member] | Fair Value, Measurements, Recurring [Member] | Forward Foreign Exchange Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts	1,002
Level III [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Total financial assets	0	0
Level III [Member] | Fair Value, Measurements, Recurring [Member] | Bank Deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Short-term investments	0	0
Level III [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Level III [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Cash equivalents	0	0
Level III [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Short-term investments	0	0
Level III [Member] | Fair Value, Measurements, Recurring [Member] | Forward Foreign Exchange Contracts [Member] | Accrued and Other Current Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Accrued and other current liabilities - Forward foreign exchange contracts	$ 0