Credit Facilities (Narrative) (Details)			12 Months Ended
	Mar. 13, 2019 USD ($) property	Mar. 02, 2018 USD ($) property	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2019	Dec. 31, 2019 encumbered_property	Nov. 01, 2019 USD ($) instrument	Oct. 30, 2019 instrument	Apr. 15, 2019	Oct. 31, 2016 instrument
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity			55.00%
Number of properties			193					102
Effective Interest Rate				4.76%			4.14%
Credit facilities, net				$ 602,622,000		$ 605,269,000
Notional Amount									$ 88,700,000
Proceeds from credit facilities			$ 225,618,000	147,753,000	$ 380,170,000
Repayments of credit facility borrowings			$ 368,300,000	$ 80,000,000	326,800,000
Term Loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 150,000,000.0
Effective Interest Rate							4.05%
Long-term debt						150,000,000.0
Mortgage Notes Payable
Line of Credit Facility [Line Items]
Effective Interest Rate				4.48%			3.90%
Long-term debt				$ 462,839,000		528,284,000
New Credit Facilities
Line of Credit Facility [Line Items]
Long-term debt, covenant requirements, distribution in excess of modified FFO, percent			95.00%
New Credit Facilities | Term Loan
Line of Credit Facility [Line Items]
Weighted average rate											2.30%
Fannie Credit Facility | Interest rate caps
Line of Credit Facility [Line Items]
Number of Instruments | instrument									2	2		2
Interest rate cap												3.50%
Bridge Loan | Mortgage Notes Payable
Line of Credit Facility [Line Items]
Effective Interest Rate				4.87%			0.00%
Proceeds from credit facilities		$ 64,200,000
Minimum | New Credit Facilities
Line of Credit Facility [Line Items]
Long-term debt, covenant requirements, amount						50,000,000.0
London Interbank Offered Rate (LIBOR) | Minimum | Term Loan
Line of Credit Facility [Line Items]
Interest rate	1.55%
London Interbank Offered Rate (LIBOR) | Maximum | Term Loan
Line of Credit Facility [Line Items]
Interest rate	2.15%
Base Rate | Minimum | Term Loan
Line of Credit Facility [Line Items]
Interest rate	0.30%
Base Rate | Maximum | Term Loan
Line of Credit Facility [Line Items]
Interest rate	0.90%
Secured Debt
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 630,000,000.0
Remaining borrowing capacity						79,500,000
Secured Debt | Minimum
Line of Credit Facility [Line Items]
Line of credit, increase	370,000,000.0
Secured Debt | Maximum
Line of Credit Facility [Line Items]
Line of credit, increase	$ 1,000,000,000.0
Credit Facilities
Line of Credit Facility [Line Items]
Credit facilities, net				$ 0		245,947,000
Credit Facilities | Term Loan
Line of Credit Facility [Line Items]
Effective Interest Rate				0.00%
Credit facilities, net				$ 0		150,000,000
Credit Facilities | Fannie Mae Master Credit Facilities
Line of Credit Facility [Line Items]
Number of properties | property			22
Credit facilities, net				$ 359,322,000		359,322,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Number of properties | property	65
Revolving Credit Facility | Credit Facilities
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 480,000,000.0
Number of properties | property			80
Effective Interest Rate				0.00%			4.08%
Credit facilities, net				$ 0		100,618,000
Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Credit Facilities
Line of Credit Facility [Line Items]
Basis spread on variable rate, base rate calculation	1.00%
Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum | Credit Facilities
Line of Credit Facility [Line Items]
Interest rate	1.60%
Revolving Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum | Credit Facilities
Line of Credit Facility [Line Items]
Interest rate	2.20%
Revolving Credit Facility | Base Rate | Minimum | Credit Facilities
Line of Credit Facility [Line Items]
Interest rate	0.35%
Revolving Credit Facility | Base Rate | Maximum | Credit Facilities
Line of Credit Facility [Line Items]
Interest rate	0.95%
Revolving Credit Facility | Fed Funds Effective Rate Overnight Index Swap Rate | Credit Facilities
Line of Credit Facility [Line Items]
Interest rate	0.50%
Bridge Loan | Fannie Mae Master Credit Facility
Line of Credit Facility [Line Items]
Repayments of credit facility borrowings		$ 61,700,000
Capital One Facility
Line of Credit Facility [Line Items]
Number of properties | property		7
Capital One Facility | Credit Facilities | Fannie Mae Master Credit Facilities
Line of Credit Facility [Line Items]
Number of properties | property			12
Effective Interest Rate				4.83%			4.17%
Credit facilities, net				$ 216,614,000	152,500,000	216,614,000
KeyBank Facility | Credit Facilities | Fannie Mae Master Credit Facilities
Line of Credit Facility [Line Items]
Number of properties | property			10
Effective Interest Rate				4.88%			4.22%
Credit facilities, net				$ 142,708,000	$ 142,700,000	$ 142,708,000