Subsequent Events (Details)				3 Months Ended	9 Months Ended
	Oct. 31, 2017 USD ($) $ / shares shares	Oct. 27, 2017 USD ($) extension	Oct. 16, 2017 USD ($) property	Sep. 30, 2017 USD ($) Property	Sep. 30, 2017 USD ($) Property	Sep. 30, 2016 USD ($)	Dec. 31, 2016 Property
Subsequent Event [Line Items]
Number of pledged properties | Property				128	128		126
Repayments of debt				$ 6,900,000
Subsequent Event
Subsequent Event [Line Items]
Debt instrument, face amount			$ 204,000,000
Stated interest rate (in percentage)			3.97%
Number of pledged properties | property			5
Repayments of debt			$ 194,200,000
Penalty for early repayment of debt			$ 2,200,000
Private Placement
Subsequent Event [Line Items]
Total gross proceeds					$ 42,037,000	$ 50,000,000
Private Placement | Subsequent Event
Subsequent Event [Line Items]
Shares of Common Stock sold (shares) | shares	336,290
Weighted average price (usd per share) | $ / shares	$ 85.13
Total gross proceeds	$ 28,300,000
Shares remaining to be issued	$ 4,300,000
Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, face amount		$ 400,000,000
Number of extensions | extension		2
Duration of extension (in months)		6 months
Commitment and arrangement fees		$ 3,600,000
Unsecured Debt | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, face amount		$ 200,000,000
Minimum | Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Annual fees		0.15%
Minimum | LIBOR | Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Variable rate (in percentage)		1.10%
Minimum | LIBOR | Unsecured Debt | Subsequent Event
Subsequent Event [Line Items]
Variable rate (in percentage)		1.20%
Maximum | Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Annual fees		0.35%
Maximum | LIBOR | Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Variable rate (in percentage)		1.55%
Maximum | LIBOR | Unsecured Debt | Subsequent Event
Subsequent Event [Line Items]
Variable rate (in percentage)		1.90%