Derivative Financial Instruments - Changes in Net Gain or Loss on Cash Flow Hedges Included in Accumulated Other Comprehensive Loss (Details) - Interest rate swap agreements - Cash flow hedges - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Changes in Net Gain or Loss on Cash Flow Hedges Included in Accumulated Other Comprehensive Loss
Balance at the beginning of the period	$ 5,872	$ 2,290	$ 2,936
Unrealized loss (gain) recognized in other comprehensive loss, net of tax	4,775	(1,618)	7,926	$ 920
Reclassification to interest expense, net	(87)	(696)	(302)	(944)
Balance at the end of the period	$ 10,560	$ (24)	$ 10,560	$ (24)