Debt (Narrative) (Details)		3 Months Ended	12 Months Ended
	Dec. 11, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) derivative_contract	Dec. 31, 2017 USD ($)	Jan. 03, 2020 USD ($)	Mar. 27, 2019 USD ($)	Jan. 01, 2019 USD ($)	Mar. 30, 2016 USD ($) debt_extension
Debt Instrument [Line Items]
Debt service guaranty liability			$ 57,380,000	$ 60,900,000
Principal payments of debt			55,556,000	257,028,000	$ 28,723,000
Gain (loss) on debt extinguishment		$ 3,800,000		400,000
Debt instruments collateral value			500,000,000	600,000,000
Unsecured notes payable under credit facilities			0	5,000,000
Finance lease obligations			21,804,000					$ 21,900,000
Capital leases				21,898,000
Net premium (discount) on debt			(3,900,000)
Deferred debt costs			(5,500,000)
Non-cash debt			$ 1,500,000
Debt Service Guaranty [Member]
Debt Instrument [Line Items]
Debt coverage ratio			1.4
Mortgages [Member]
Debt Instrument [Line Items]
Debt stated interest rate			7.00%
Principal payments of debt			$ 50,000,000
Par Value Debt [Member]
Debt Instrument [Line Items]
Principal payments of debt				51,000,000.0
Unsecured Variable-Rate Term Loan [Member] | Unsecured Debt [Member]
Debt Instrument [Line Items]
Debt instrument, repurchased face amount				$ 200,000,000
Debt instrument, interest rate, effective percentage				2.50%
Unsecured Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit facility	$ 500,000,000								$ 500,000,000
Number of credit facility 6-month extensions | debt_extension									2
Line of credit facility, extension period	6 months
Bids amount (up to)			250,000,000
Increase in credit facility amount (up to)			$ 850,000,000
Line of credit facility, commitment fee percentage			0.15%	0.15%
Unsecured notes payable under credit facilities			$ 0	$ 5,000,000
Unsecured Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Borrowing margin over LIBOR, basis points			0.825%	0.90%
Line of Credit [Member] | Short-Term Unsecured Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit facility							$ 10,000,000
Debt instrument, term			30 days	30 days
Line of credit facility, commitment fee percentage			0.10%	0.10%
Facility fees, basis points			0.05%	0.05%
Line of Credit [Member] | Thirty-Day LIBOR [Member] | Short-Term Unsecured Facility [Member]
Debt Instrument [Line Items]
Borrowing margin over LIBOR, basis points			1.25%	1.25%
Subsequent Event [Member] | Line of Credit [Member] | Short-Term Unsecured Facility [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity under credit facility						$ 10,000,000
Financial Standby Letter of Credit [Member]
Debt Instrument [Line Items]
Held-to-maturity, restricted			$ 5,300,000	$ 5,200,000
Guarantor obligations, maximum exposure, undiscounted			$ 5,000,000.0
Interest Rate Contracts [Member] | Cash Flow Hedging [Member]
Debt Instrument [Line Items]
Number of interest rate derivatives terminated | derivative_contract				3
Notional amount of interest rate fair value hedge derivatives				$ 200,000,000
Gain due to the probability that the related hedged forecasted transactions would no longer occur				$ 3,400,000