Financial Instruments and Fair Values - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Interest rate swap agreements liability	$ 5,243	$ 436
Unrealized loss on valuation of interest rate swap agreements			$ 3,054
Loss from derivative financial instruments	0	289	0
Interest rate swaps
Derivative [Line Items]
Interest rate swap agreements liability	5,300
Designated as Hedging Instrument | Cash Flow Hedging
Derivative [Line Items]
Unrealized loss on valuation of interest rate swap agreements	900	10,500
Loss expected to be reclassified within twelve months	900
Loss from derivative financial instruments		300
Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Notional amount	515,000	265,000
Unrealized loss on valuation of interest rate swap agreements			$ 3,054
Prepaid expenses and other assets | Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Interest rate swap agreements asset	2,500
Accounts payable and accrued expenses | Designated as Hedging Instrument | Cash Flow Hedging | Interest rate swaps
Derivative [Line Items]
Interest rate swap agreements liability	$ 5,200	$ 400