Derivative Financial Instruments (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Unrealized loss on forward starting swaps/Interest rate swaps	$ (1,904,000)	$ 7,877,000
Expected net decrease to interest expense	(1,300,000)
Derivatives designated as cash flow hedges in prepaid expenses and other assets:
Interest rate swaps	659,000		$ 1,146,000
Derivatives designated as cash flow hedges in accounts payable, accrued expenses and other liabilities:
Interest rate swaps	0		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	(1,904,000)	7,877,000
Amount of gains reclassified out of accumulated other comprehensive income into interest expense:
Interest rate swaps	(515,000)	$ (106,000)
4.20% (4.234% effective rate) Notes due 2029 [Member]
Derivative [Line Items]
Principal debt amount	$ 350,000,000.00
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)