Derivative Financial Instruments (Details) - USD ($)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Derivative [Line Items]
Unrealized loss on forward starting swaps/Interest rate swaps	$ (646,000)		$ 862,000	$ (2,550,000)	$ 8,739,000
Expected net decrease to interest expense	1,000,000.0			1,000,000.0
Derivatives designated as cash flow hedges in prepaid expenses and other assets:
Interest rate swaps	0			0		$ 1,146,000
Derivatives designated as cash flow hedges in accounts payable, accrued expenses and other liabilities:
Interest rate swaps	86,000			86,000		3,581,000
Amount of unrealized gains/(losses) recognized in accumulated other comprehensive income on derivatives:
Unrealized loss on forward starting swaps/Interest rate swaps	(646,000)		862,000	(2,550,000)	8,739,000
Amount of gains reclassified out of accumulated other comprehensive income into interest expense:
Interest rate swaps	$ (360,000)		$ (515,000)	$ (875,000)	$ (621,000)
4.20% (4.234% effective rate) Notes due 2029 [Member]
Derivative [Line Items]
Principal debt amount		$ 350,000,000.0
Interest rate (in hundredths)		4.20%
Scheduled maturity date		Apr. 15, 2029
Forward Starting Swaps [Member]
Derivative [Line Items]
Amount of borrowings, subject to swaps						$ 225,000,000.0
Underlying treasury rate term (in periods)						10 years
Underlying treasury rate locked by forward-starting swaps (in hundredths)						2.86%
Unrealized loss on forward starting swaps/Interest rate swaps		$ (5,100,000)
Amount of unrealized gains/(losses) recognized in accumulated other comprehensive income on derivatives:
Unrealized loss on forward starting swaps/Interest rate swaps		$ (5,100,000)