Income Taxes - Total Balance of Unrecognized Gross Tax Benefits Resulting from R&D Credits Claimed (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Unrecognized tax benefits at beginning of year	$ 551us-gaap_UnrecognizedTaxBenefits	$ 253us-gaap_UnrecognizedTaxBenefits	$ 267us-gaap_UnrecognizedTaxBenefits
Additions (reductions) based on current year tax positions	226	298	(14)
Unrecognized tax benefits at end of year	$ 777us-gaap_UnrecognizedTaxBenefits	$ 551us-gaap_UnrecognizedTaxBenefits	$ 253us-gaap_UnrecognizedTaxBenefits

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Unrecognized Tax Benefit

-URI http://asc.fasb.org/extlink&oid=6527854

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15A

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

Name:	us-gaap_UnrecognizedTaxBenefits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant