Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Nominal or face amount used to calculate payment on derivative.

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Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Derivative Instruments - Interest rate swap agreement (Details) - Interest rate contract $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) agreement	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) agreement	Sep. 30, 2018 USD ($)	Oct. 03, 2019 USD ($)	Dec. 31, 2018 USD ($)
Derivative [Line Items]
Borrowings at variable interest rates	$ 384,000		$ 384,000			$ 427,000
Number of interest rate swap agreements \| agreement	1		1
Derivative, notional amount	$ 100,000		$ 100,000			100,000
Remaining maturity term			19 months
Net fair value of swap liability	245		$ 245
Net fair value of swap asset						$ 1,700
Gain (loss) recorded to net finance costs	$ 100	$ 100	$ 500	$ 200
Subsequent Event
Derivative [Line Items]
Derivative, notional amount					$ 100,000