Income taxes - Common Distributions (Details) - $ / shares	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Distributions Paid [Abstract]
Ordinary income	$ 0.000	$ 0.080	$ 0.240
Capital gain	0.000	0.240	0.000
Return of capital	0.069	0.150	2.690
Total distributions per share	$ 0.069	$ 0.470	$ 2.930

Taxable Return of Capital Included in Common Distribution, Per Share

No definition available.

Name:	ivtp_TaxableReturnOfCapitalIncludedInCommonDistributionPerShare
Namespace Prefix:	ivtp_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration