Financial Instruments and Fair Values - Narrative (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) derivative	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) derivative
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	$ 0		$ 436,000
Unrealized gain on valuation of interest rate swap agreements	4,180,000	$ 1,394,000
Loss from derivative financial instruments	0	247,000
Designated as Hedging Instrument | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred losses on terminated hedges	14,800,000		$ 15,100,000
Loss expected to be reclassified within twelve months	$ 1,500,000
Loss from derivative financial instruments		200,000
Notional amount, terminated		20,000,000
Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, number of instruments held | derivative	1		1
Notional amount	$ 265,000,000		$ 265,000,000.0
Unrealized gain on valuation of interest rate swap agreements	4,800,000	$ 1,400,000
Amount expected to be reclassified within twelve months	40,000
Prepaid expenses and other assets | Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements asset	$ 4,100,000
Accounts payable and accrued expenses | Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability			$ 400,000