Securities Purchase Agreement - Summary of Change to Fair Value of Warrant (Detail) (USD $) In Thousands, unless otherwise specified	0 Months Ended	1 Months Ended	12 Months Ended			4 Months Ended
	Nov. 17, 2014	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Change in fair value of warrant liability and fair value of beneficial conversion feature on convertible Series C preferred shares			$ 3,280	$ 0	$ 0
Reclassification to additional paid-in-capital	(8,219)	(8,219)	(8,219)
Level 3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at September 8, 2014 (Transaction Date)	8,219	8,219				4,939
Change in fair value of warrant liability and fair value of beneficial conversion feature on convertible Series C preferred shares						3,280
Ending balance at December 31, 2014	$ 8,219	$ 0	$ 0			$ 0