Derivative Instruments - Cash flow hedges (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Effects of derivative instruments
Unrealized loss on derivative instruments	$ (2,298)	$ (3,331)
Cash flow hedging
Effects of derivative instruments
Unrealized loss on derivative instruments	2,298	3,331
Cash flow hedging \| Interest rate contracts \| Interest expense
Effects of derivative instruments
Unrealized loss on derivative instruments	$ 2,298	$ 3,331

Amount, before tax and after reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness, attributable to parent.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580

Name:	us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossAfterReclassificationBeforeTaxParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration