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Debt (Narrative) (Details)	Mar. 22, 2019 USD ($)	Jan. 31, 2019 USD ($)	Nov. 07, 2014 USD ($)	Mar. 31, 2019 USD ($) property	May 26, 2017 USD ($)
Debt Instrument [Line Items]
Secured debt				$ 172,300,000
Number of collateralized properties (in collateralized properties) \| property				8
Carrying value of collateralized properties				$ 273,000,000
2019 Facility [Member]
Debt Instrument [Line Items]
Credit facility, covenant, total debt to total assets ratio, maximum		0.60
Credit facility, covenant, secured debt to total asset ratio, maximum		0.40
Credit facility, covenant, EBITDA to fixed charges ratio, minimum		1.50
Credit facility, covenant, other recourse debt to total assets ratio, maximum		0.15
Credit facility, interest rate at period end				4.14%
Covenant, tangible net worth threshold before percentage of aggregate net proceeds, amount		$ 372,000,000
Covenant, tangible net worth, percentage of aggregate net proceeds, minimum		75.00%
Repayments of Long-term Debt		$ 446,200,000
Series A Senior Notes [Member]
Debt Instrument [Line Items]
Annual principal payment	$ 7,100,000
Series B Senior Notes [Member]
Debt Instrument [Line Items]
Annual principal payment	10,000,000
Senior notes
Debt Instrument [Line Items]
Face amount of debt	100,000,000
Periodic payment, principal	$ 1,000,000
Credit facility, covenant, total debt to total assets ratio, maximum	0.60
Credit facility, covenant, secured debt to total asset ratio, maximum	0.40
Credit facility, covenant, EBITDA to fixed charges ratio, minimum	1.50
Credit facility, covenant, other recourse debt to total assets ratio, maximum	0.15
Covenant, tangible net worth threshold before percentage of aggregate net proceeds, amount	$ 372,000,000
Covenant, tangible net worth, percentage of aggregate net proceeds, minimum	75.00%
Senior notes \| Series A Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 50,000,000
Stated interest rate	5.09%
Senior notes \| Series B Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 50,000,000
Stated interest rate	5.17%
Fixed rate notes \| $80.0 million, 3.72% Note, due June 1, 2027
Debt Instrument [Line Items]
Face amount of debt				$ 80,000,000	$ 80,000,000
Stated interest rate				3.72%	3.72%
Revolving Credit Facility [Member] \| 2019 Facility [Member]
Debt Instrument [Line Items]
Line of credit outstanding				$ 351,000,000
Credit facility, remaining borrowing capacity				$ 164,000,000
Revolving Credit Facility [Member] \| 2019 Facility [Member] \| LIBOR Rate
Debt Instrument [Line Items]
Basis spread on variable rate			1.00%
Revolving Credit Facility [Member] \| 2019 Facility [Member] \| LIBOR Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			1.40%
Revolving Credit Facility [Member] \| 2019 Facility [Member] \| LIBOR Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.90%
Revolving Credit Facility [Member] \| 2018 Facility [Member] \| LIBOR Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.95%
Revolving Credit Facility [Member] \| The Revolver [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity			$ 300,000,000
Term Loan [Member] \| 2019 Facility [Member] \| LIBOR Rate \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate			1.35%
Term Loan [Member] \| 2019 Facility [Member] \| LIBOR Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			1.90%
Term Loan [Member] \| 2018 Facility [Member] \| LIBOR Rate \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate			2.25%
Term Loan [Member] \| Term Loan 1 [Member]
Debt Instrument [Line Items]
Face amount of debt			$ 50,000,000
Term Loan [Member] \| Term Loan 2 [Member]
Debt Instrument [Line Items]
Face amount of debt			50,000,000
Term Loan [Member] \| Term Loan 3 [Member]
Debt Instrument [Line Items]
Face amount of debt			$ 100,000,000
Term Loan [Member] \| Unsecured Line Of Credit [Member] \| Term Loan A [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		165,000,000
Term Loan [Member] \| Unsecured Line Of Credit [Member] \| Term Loan B [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		100,000,000
Revolving Credit Facility [Member] \| 2019 Facility [Member]
Debt Instrument [Line Items]
Credit facility, accordion feature, increase limit		200,000,000
Revolving Credit Facility [Member] \| Unsecured Line Of Credit [Member] \| 2019 Revolver [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity		$ 250,000,000