Changes in Estimated Fair Value of Convertible Note Payable (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in estimated fair value of convertible note payable	$ 1,785	$ 671	$ 614	$ (3,787)
Fair Value, Inputs, Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2013			11,279
Change in estimated fair value of convertible note payable			(614)
Balance at September 30, 2014	$ 10,665		$ 10,665