Stockholders Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	Sep. 30, 2014
Stockholders' Equity Note [Abstract]
Dollar value of shares registered in public offering, distribution reinvestment plan	$ 600.0
Offering price per share, distribution reinvestment plan	$ 9.88
Dollar value of shares remaining in public offering, distribution reinvestment plan	$ 567.5

The total dollar amount in shares remaining available for sale pursuant to a public offering.

No definition available.

Name:	ck0001464720_DollarAmountRemainingInPublicOffering
Namespace Prefix:	ck0001464720_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant