Fair Value Measures and Financial Instruments - Additional Information (Details)	6 Months Ended		12 Months Ended
	Jun. 30, 2015 USD ($) Property	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Property
Fair Value Inputs Assets Quantitative Information [Line Items]
Properties acquired | Property			32
Properties acquired for cash	$ 164,577,909	$ 187,864,183	$ 633,200,000
Purchased price of land			129,320,000
Building, building improvements, furniture, fixtures and equipment			485,996,000
Intangible lease assets gross			$ 17,884,000
Derivatives cap weighted average interest rate	6.00%
Earnings ineffectiveness to derivatives designated as cash flow hedges	$ 0
Change in fair value on hedging derivative instruments	$ 395,631	$ 0
Debt With Floating Interest Rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Interest rate on variable rate loans	2.01%		2.02%
Debt With Fixed Interest Rate
Fair Value Inputs Assets Quantitative Information [Line Items]
Fixed rate debt, minimum	3.70%
Fixed rate debt, maximum	3.90%
Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Interest rate caps term range	3 years
Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Interest rate caps term range	4 years
Additional Real Estate Properties Acquisition
Fair Value Inputs Assets Quantitative Information [Line Items]
Properties acquired | Property	7
Properties acquired for cash	$ 183,588,400
Purchased price of land	35,890,000
Building, building improvements, furniture, fixtures and equipment	142,866,400
Intangible lease assets gross	$ 4,832,000
Level 2 Inputs
Fair Value Inputs Assets Quantitative Information [Line Items]
Properties acquired | Property			3
Level 2 Inputs | Additional Real Estate Properties Acquisition
Fair Value Inputs Assets Quantitative Information [Line Items]
Properties acquired | Property	1