Financial Instruments and Fair Values - Effect of Derivative Financial Instruments Designated as Cash Flow Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in other comprehensive income (loss)	$ (95)	$ (1,709)	$ (36)	$ (19,404)
Amount of gain (loss) reclassified from accumulated other comprehensive (loss) into interest expense	(2,898)	(2,317)	(5,767)	(3,113)
Interest expense	(23,422)	(23,928)	(46,976)	(43,546)
Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in other comprehensive income (loss)	(95)	(1,709)	(36)	(19,404)
Amount of gain (loss) reclassified from accumulated other comprehensive (loss) into interest expense	(2,898)	(2,317)	(5,767)	(3,113)
Interest rate swap | Reclassification out of accumulated other comprehensive income | Accumulated other comprehensive income (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Interest expense	$ (2,898)	$ (2,317)	$ (5,767)	$ (3,113)