Financial Instruments and Fair Values - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	$ 13,378,000		$ 13,378,000		$ 5,591,000
Change in unrealized gain (loss) on valuation of interest rate swap agreements	(1,279,000)	$ 930,000	(14,252,000)	$ (29,305,000)
Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swap agreements liability	13,400,000		13,400,000
Designated as Hedging Instrument | Cash Flow Hedging
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in unrealized gain (loss) on valuation of interest rate swap agreements	(1,600,000)	$ 900,000	(14,700,000)	$ (29,300,000)
Amount expected to be reclassified within twelve months			2,900,000
Designated as Hedging Instrument | Cash Flow Hedging | Interest Rate Swap
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	790,000,000		790,000,000
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	$ 13,400,000		$ 13,400,000		5,600,000
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					$ 600,000