Fair Value Measurement - Additional Information (Detail) (IPO)	12 Months Ended
Dec. 31, 2014
IPO
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Initial public offering closing date	Apr. 04, 2014

Date the subsidiary or equity investee issued or sold stock, in CCYY-MM-DD format.

No definition available.

Name:	us-gaap_SaleOfStockTransactionDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration