Indebtedness - Scheduled Principal Repayments and Term-loan Maturities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Principal repayments and maturities
2018	$ 77,683
2019	13,284
2020	10,338
2021	176,347
2022	169,808
Thereafter	75,952
Total	523,412	$ 527,082
Monthly Principal Amortization
Principal repayments and maturities
2018	4,361
2019	3,951
2020	4,959
2021	4,073
2022	2,699
Thereafter	70,385
Total	90,428
Balloon Payments At Loan Maturity
Principal repayments and maturities
2018	73,322
2019	9,333
2020	5,379
2021	172,274
2022	167,109
Thereafter	5,567
Total	$ 432,984

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section S99
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Section S99
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-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690

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