Refers to an additional period of time to issue notes.

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Represents the restrictions on investments, change of control provisions and provisions, expressed as a percentage of total assets to be disposed off as per the financial covenant.

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Represents the number of tranches related to issuance of debt.

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The period of time specific payments are to be made per the agreement.

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Represents the amount of prepayment to be paid on the debt instrument.

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- Definition

Represents the percentage of debt outstanding in which the interest rate was effectively exchanged

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No definition available.

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The annual fee percentage based on any issued and outstanding letters of credit under the facility.

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Maximum borrowing capacity under the credit facility with the accordion feature.

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Indicates the number of assets pledged under the loan plan.

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Number of mortgages outstanding.

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The amount that the debt instrument can increase per the accordian feature.

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No definition available.

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- Definition

Amount of liabilities assumed at the acquisition date.

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Amount of the total principal payments made during the annual reporting period.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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No definition available.

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Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Amount of the required periodic payments applied to principal.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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No definition available.

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Weighted average interest rate of debt outstanding.

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No definition available.

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Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Fixed interest rate related to the interest rate derivative.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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Amount of cash outflow for cost from early extinguishment and prepayment of debt. Includes, but is not limited to, third-party cost, premium paid, and other fee paid to lender directly for debt extinguishment or debt prepayment. Excludes accrued interest.

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Credit Arrangements - Narrative (Details) $ in Thousands, $ in Millions			3 Months Ended	9 Months Ended	12 Months Ended		34 Months Ended
	Aug. 03, 2018 USD ($)	Jun. 03, 2015 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) building	Nov. 09, 2015 USD ($) item	Dec. 31, 2018 CAD ($) loan	Dec. 31, 2018 USD ($) loan	Sep. 30, 2017 USD ($)	Sep. 29, 2017 USD ($)	Sep. 28, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 loan	Jul. 25, 2013 USD ($)	Dec. 28, 2012 USD ($)
Credit arrangements
Weighted average interest rate (as a percent)						3.00%		4.10%	4.10%
Mortgages
Credit arrangements
Interest rate (as a percent)						5.00%		4.50%	4.50%
Principal amount									$ 16,500
Number Of Mortgages \| loan								2	2
Number of assets secured \| building						3
Assumed notes						$ 4,200
Secured mortgage notes, maturing on January 1, 2031
Credit arrangements
Interest rate (as a percent)														4.30%
Principal amount													$ 8,000
Number Of Mortgages \| loan														2
Senior secured notes
Credit arrangements
Interest rate (as a percent)							4.60%								3.85%	3.65%
Principal amount							$ 25,000								$ 25,000	$ 50,000
Number of tranches \| item							3
Prepayment penalty			$ 2,300
Notes Agreement
Credit arrangements
Principal amount																$ 25,000
Notes Agreement \| Minimum
Credit arrangements
Restrictions on investments, change of control provisions and provisions as a percentage of total assets to be disposed off					20.00%
Notes Agreement \| Maximum
Credit arrangements
Principal amount		$ 75,000
Commercial Equipment Notes \| Minimum
Credit arrangements
Interest rate (as a percent)								1.83%	1.83%
Commercial Equipment Notes \| Maximum
Credit arrangements
Interest rate (as a percent)								4.40%	4.40%
Credit Agreement
Credit arrangements
Maximum borrowing capacity											$ 200,000	$ 125,000
Potential increase per the accordion feature	$ 75,000
Debt issuance costs			$ 1,000	$ 1,000						$ 600
Additional Period to Issue Notes		3 years
Available borrowing capacity									$ 147,000
Credit Agreement \| Federal funds rate
Credit arrangements
Basis spread on variable rate (as a percent)					0.50%
Credit Agreement \| Minimum
Credit arrangements
Prepayment to be paid on debt					$ 5,000
Restrictions on investments, change of control provisions and provisions as a percentage of total assets to be disposed off					20.00%
Credit Agreement \| Credit Agreement
Credit arrangements
Maximum borrowing capacity									200,000
Maximum borrowing capacity with accordion feature									250,000
Credit Agreement \| Commercial letters of credit
Credit arrangements
Commercial letters of credit outstanding									53,000
Term Loan
Credit arrangements
Principal amount	220,000
Interest rate swap agreement				75.00%
Derivative fixed interest rate (as a percent)			2.886%	2.886%
Term Loan \| LIBOR
Credit arrangements
Basis spread on variable rate (as a percent)					2.00%
Term Loan \| First Three Years
Credit arrangements
Quarterly principal payment	2,750
Annual principal payments	$ 11,000
Number of years payments are to be made	3 years
Term Loan \| Next Two Years
Credit arrangements
Quarterly principal payment	$ 4,125
Annual principal payments	$ 16,500
Canadian Credit Facility
Credit arrangements
Available borrowing capacity								$ 4.0
Canadian Credit Facility \| Commercial letters of credit
Credit arrangements
Maximum borrowing capacity								$ 8.0	$ 4,000
Annual fee (as a percent)					1.00%
Canadian Credit Facility \| Commercial letters of credit \| Maximum
Credit arrangements
Term of credit facility					5 years