Summary Information Concerning Indebtedness (Parenthetical) (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2017		Dec. 31, 2016
Debt Instrument [Line Items]
Outstanding Principal	$ 771,553,000		$ 750,188,000
Derivative, notional amount	350,000,000		350,000,000
Secured Credit Facility
Debt Instrument [Line Items]
Secured credit facility borrowing capacity	312,500,000		312,500,000
Outstanding Principal	172,000,000	[1],[2]	$ 150,000,000	[3]
Interest Rate Swap
Debt Instrument [Line Items]
Derivative, notional amount	$ 150,000,000
Derivative, maturity date	Jun. 17, 2021
Derivative, fixed interest rate	1.145%

[1] As of March 31, 2017, IRT maintained a float-to-fixed interest rate swap with a $150,000 notional amount. This swap, which expires on June 17, 2021 and has a fixed rate of 1.145%, has converted $150,000 of our floating rate debt to fixed rate debt.

[2] The secured credit facility total capacity is $312,500, of which $172,000 was outstanding as of March 31, 2017.

[3] The secured credit facility total capacity was $312,500, of which $150,000 was outstanding as of December 31, 2016.