Long-Term Debt - Effects of Interest Rate Swap and Cap Agreements (Details) - Cash Flow Hedging - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Amount of unrealized losses in OCI on interest rate cap and swap agreements	$ (133)	$ (5,437)	$ (3,670)
Amount of losses reclassified from accumulated OCI into income	6,286	5,058	2,566
Tax benefit (expense)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of unrealized losses in OCI on interest rate cap and swap agreements	48	3,460	2,343
Amount of losses reclassified from accumulated OCI into income	(2,180)	(3,220)	(1,632)
Interest rate cap agreements | Debt Expense (Including Refinancing Charges)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of unrealized losses in OCI on interest rate cap and swap agreements	(181)	(8,897)	(5,198)
Amount of losses reclassified from accumulated OCI into income	8,466	8,278	3,899
Interest rate swap agreements | Debt Expense (Including Refinancing Charges)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of unrealized losses in OCI on interest rate cap and swap agreements	0	0	(815)
Amount of losses reclassified from accumulated OCI into income	$ 0	$ 0	$ 299