Financial Instruments: Derivatives and Hedging - Interest Rate Swaps (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations	$ 10,054	$ 8,980	$ 18,654	$ 18,043
Interest rate swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations			18,654	18,043
Interest rate swap | Amounts of previously recorded gain/(loss) reclassified from OCI into Interest Expense
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations			(5,344)	(2,163)
Interest rate swap | Amounts of gain (loss) recognized in OCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total amount of Interest Expense presented in the consolidated statements of operations			$ 2,542	$ (20,439)