Estimate of Fair Value of Secured Debt Obligations (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 TriplePoint - May 2014 Advance Principal Balance	Sep. 30, 2014 TriplePoint - May 2014 Advance Change in Estimated Fair Value	Dec. 31, 2013 TriplePoint - September 2010 Advance Principal Balance	Dec. 31, 2013 TriplePoint - September 2010 Advance Change in Estimated Fair Value	Dec. 31, 2013 TriplePoint - October 2011 Advance Principal Balance	Dec. 31, 2013 TriplePoint - October 2011 Advance Change in Estimated Fair Value	Dec. 31, 2013 TriplePoint - January 2012 Advance Principal Balance	Dec. 31, 2013 TriplePoint - January 2012 Advance Change in Estimated Fair Value
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Debt instrument fair value	$ 897	$ 839	$ 917	$ 847	$ 6,657	$ 5,942	$ 3,495	$ 3,079