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Mortgage Loan (Details) $ in Thousands											9 Months Ended
Mortgage Loan (Details) $ in Thousands	Sep. 22, 2017 USD ($) ft² building	Aug. 30, 2017 USD ($)	Jul. 14, 2017 USD ($) ft²	Mar. 15, 2017 USD ($) ft² building	Nov. 17, 2016 USD ($) ft² derivative	Apr. 26, 2016 USD ($) ft² building	Dec. 11, 2015 USD ($) ft² derivative subsidiary	Dec. 10, 2015 USD ($) subsidiary	Sep. 01, 2015 USD ($) ft²	Dec. 31, 2014 USD ($) ft²	Aug. 31, 2017 USD ($) ft² item	Aug. 31, 2016 USD ($)	Sep. 21, 2017 USD ($)	Nov. 30, 2016 USD ($)	Nov. 30, 2009
Long-Term Debt
Mortgage loans, prior to debt issuance costs											$ 133,330			$ 111,139
Debt issuance costs, net											(1,766)			(1,442)
Mortgage loans, net											131,564			109,697
Debt disclosures
Other assets											18,596			15,163
Payment for termination of interest rate swap agreement											341
Proceeds from issuance of debt											34,750	$ 18,800
Funds placed in (returned from) escrow												(600)
Ineffectiveness on cash flow hedges											0
Anticipated ineffectiveness on cash flow hedges											0
Net fair value of interest rate swap agreements											2,429
Other assets
Debt disclosures
Net fair value of interest rate swap agreements											18
Other liabilities caption
Debt disclosures
Net fair value of interest rate swap agreements											2,447
Accounting Standards Update 2015-03 [Member] \| Restatement Adjustment [Member]
Long-Term Debt
Mortgage loans, net														(1,442)
Debt disclosures
Other assets														(1,442)
Nonrecourse variable rate loans, due October 2, 2017
Long-Term Debt
Mortgage loans, prior to debt issuance costs											5,892			6,034
Mortgage loans, net													$ 5,876
Debt disclosures
Number of buildings used as collateral \| building	2
Area of collateralized properties (in square feet) \| ft²	161,000
Fixed interest rate pursuant to interest rate swap agreement (as a percent)	3.86%
Cash on hand	$ 1,000
Prepayment using funds released from escrow	501
Nonrecourse variable rate loans, due February 1, 2019
Long-Term Debt
Mortgage loans, prior to debt issuance costs														10,313
Mortgage loans, net			$ 10,120
Debt disclosures
Area of collateralized properties (in square feet) \| ft²			304,000
Variable interest rate margin (as a percent)			2.75%
Fixed interest rate pursuant to interest rate swap agreement (as a percent)			6.35%
Nonrecourse variable rate loans, due August 1, 2019
Long-Term Debt
Mortgage loans, prior to debt issuance costs						$ 7,418
Debt disclosures
Number of buildings used as collateral \| building						4
Area of collateralized properties (in square feet) \| ft²						240,000
Nonrecourse variable rate loans, due January 27, 2020
Long-Term Debt
Mortgage loans, prior to debt issuance costs											3,510			3,606
Nonrecourse variable rate loans, due January 2, 2025
Long-Term Debt
Mortgage loans, prior to debt issuance costs											20,353			20,744
Debt disclosures
Proceeds from issuance of debt										$ 10,891
Term of debt							10 years
Number of subsidiaries which are party to the mortgage \| subsidiary							2
Debt amount refinanced										$ 8,859
Nonrecourse variable rate mortgage, due September 1, 2025
Debt disclosures
Leased space \| ft²									196,000
Number of subsidiaries which are party to the mortgage \| subsidiary								1
Nonrecourse Variable Rate Mortgage, Refinanced, Due In September 2026 [Member]
Long-Term Debt
Mortgage loans, prior to debt issuance costs					$ 26,725
Debt disclosures
Proceeds from issuance of debt					$ 13,000
Term of debt					10 years
Debt amount refinanced					$ 13,725
Nonrecourse variable rate mortgage, due May 1, 2026
Long-Term Debt
Mortgage loans, prior to debt issuance costs											13,930			14,187
Debt disclosures
New mortgage						$ 14,350
Number of buildings used as collateral \| building						4
Proceeds from issuance of debt						$ 6,932
Term of debt						10 years
Amortization period of debt						25 years
Additional area serving as collateral \| ft²						98,000
Nonrecourse variable rate mortgage, due November 17, 2026
Long-Term Debt
Mortgage loans, prior to debt issuance costs											26,241			26,725
Nonrecourse variable rate mortgage, due March 1, 2027
Long-Term Debt
Mortgage loans, prior to debt issuance costs											11,891
Nonrecourse variable rate mortgage, due August 1, 2027
Long-Term Debt
Mortgage loans, prior to debt issuance costs											10,581
Debt disclosures
New mortgage			$ 10,600
Variable interest rate margin (as a percent)			2.05%
Fixed interest rate pursuant to interest rate swap agreement (as a percent)			4.39%
Payment for termination of interest rate swap agreement			$ 341
Term of debt			10 months
Amortization period of debt			25 years
3.97%, due September 1, 2027
Long-Term Debt
Mortgage loans, prior to debt issuance costs		$ 12,150									$ 12,150
Interest rate (as a percent)		3.97%									3.97%
Debt disclosures
Term of debt		10 years
5.09%, due July 1, 2029 GCD mortgage loan
Long-Term Debt
Mortgage loans, prior to debt issuance costs											$ 6,700			7,001
Interest rate (as a percent)											5.09%
5.09%, due July 1, 2029 TD mortgage Loan
Long-Term Debt
Mortgage loans, prior to debt issuance costs											$ 4,694			4,905
Interest rate (as a percent)											5.09%
4.33%, due August 1, 2030 mortgage loan
Long-Term Debt
Mortgage loans, prior to debt issuance costs											$ 17,388			$ 17,624
Interest rate (as a percent)											4.33%
2017 PUB Mortgage
Debt disclosures
New mortgage				$ 12,000
Number of buildings used as collateral \| building				2
Area of collateralized properties (in square feet) \| ft²				275,000
Term of debt				10 years
Amortization period of debt				25 years
Number of buildings subject to master lease \| building				1
2017 Webster Loan
Long-Term Debt
Mortgage loans, prior to debt issuance costs	$ 4,375
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)	4.72%
Term of debt	5 years
Amortization period of debt	25 years
First Collateralized Property \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Area of collateralized properties (in square feet) \| ft²											303,000
First Collateralized Property \| Nonrecourse variable rate mortgage, due September 1, 2025
Debt disclosures
Area of collateralized properties (in square feet) \| ft²											280,000
First Collateralized Property \| Nonrecourse variable rate mortgage, due May 1, 2026
Debt disclosures
Leased space \| ft²						58,000
Second Collateralized Property \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Area of collateralized properties (in square feet) \| ft²											228,000
Leased space \| ft²										201,000
Second Collateralized Property \| Nonrecourse Variable Rate Mortgage, Refinanced, Due In September 2026 [Member]
Debt disclosures
Area of collateralized properties (in square feet) \| ft²					252,000
Second Collateralized Property \| Nonrecourse variable rate mortgage, due May 1, 2026
Debt disclosures
Leased space \| ft²						40,000
Interest rate swap agreement
Debt disclosures
Number of agreements containing credit risk related contingent features \| item											0
Recognized net losses (included in other comprehensive loss), before taxes, on interest rate swap agreements											$ 1,045	$ 2,898
Loss expected to be reclassified over next twelve months from accumulated other comprehensive loss to interest expense											$ 1,101
Interest rate swap agreement \| Nonrecourse variable rate loans, due August 1, 2019
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)															6.58%
Interest rate swap agreement \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)							4.39%
Number of interest rate swap derivatives \| derivative							2
Interest rate swap agreement \| Nonrecourse Variable Rate Mortgage, Refinanced, Due In September 2026 [Member]
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)					3.79%
Number of interest rate swap derivatives \| derivative					2
Interest rate swap agreement \| Nonrecourse variable rate mortgage, due May 1, 2026
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)						4.17%
Interest rate swap agreement \| 2017 PUB Mortgage
Debt disclosures
Fixed interest rate pursuant to interest rate swap agreement (as a percent)				4.45%
Notional amount of interest rate swap agreement				$ 12,000
Nonrecourse Mortgage, Proceeds Excluding Contingent Portion [Member] \| Nonrecourse variable rate mortgage, due September 1, 2025
Debt disclosures
Proceeds from issuance of debt									$ 11,500
Nonrecourse Mortgage, Proceeds Excluding Contingent Portion [Member] \| Second Collateralized Property \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Leased space \| ft²							102,000
Nonrecourse Mortgage, Contingent Portion [Member] \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Proceeds from issuance of debt							$ 1,850
Nonrecourse Mortgage, Contingent Portion [Member] \| Nonrecourse variable rate mortgage, due September 1, 2025
Debt disclosures
Proceeds from issuance of debt								$ 2,600
LIBOR \| Nonrecourse variable rate loans, due August 1, 2019
Debt disclosures
Variable interest rate margin (as a percent)						3.08%
LIBOR \| Nonrecourse variable rate loans, due January 2, 2025
Debt disclosures
Variable interest rate margin (as a percent)							1.95%
LIBOR \| Nonrecourse Variable Rate Mortgage, Refinanced, Due In September 2026 [Member]
Debt disclosures
Variable interest rate margin (as a percent)					1.70%
LIBOR \| Nonrecourse variable rate mortgage, due May 1, 2026
Debt disclosures
Variable interest rate margin (as a percent)						2.00%
LIBOR \| 2017 PUB Mortgage
Debt disclosures
Variable interest rate margin (as a percent)				1.95%
LIBOR \| 2017 Webster Loan
Debt disclosures
Variable interest rate margin (as a percent)	2.75%