Fair Value - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Financial instruments transferred among fair value hierarchy levels	$ 0	$ 0

Amount of financial instruments transferred among the fair value hierarchy levels (Level 1, 2, and 3).

No definition available.

Name:	ck0001464720_TransfersAmongFairValueHierarchyLevelsAmount
Namespace Prefix:	ck0001464720_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant