Cash, Cash Equivalents and Short-Term Investments - Additional Information (Detail)	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Maximum [Member]
Cash and Cash Equivalents [Line Items]
Weighted average maturity period of available-for-sale securities	1 month	4 months

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_CashAndCashEquivalentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration