Intangible Assets, Net - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets And Liabilities [Line Items]
Amortization of intangible asset	$ 0.1	$ 0.1	$ 0.1
Intangible assets, amortization expense, next twelve months	0.1
Intangible assets, amortization expense, year two	0.1
Intangible assets, amortization expense, year three	0.1
Intangible assets, amortization expense, year four	0.1
Intangible assets, amortization expense, year five	$ 0.1