Derivative Financial Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gain on forward starting interest rate swaps			$ (9,134)	$ 4,161	$ 1,732
Expected decrease to interest expense			300
Derivatives designated as cash flow hedges in prepaid expenses and other assets [Abstract]
Interest rate swaps			0	1,146
Derivatives designated as cash flow hedges in accounts payable, accrued expenses and other liabilities [Abstract]
Interest rate swaps			154	3,581
Amount of unrealized gains recognized in accumulated other comprehensive income/(loss) on derivatives (effective portion) [Abstract]
Interest rate swaps			(9,134)	4,161	1,732
Amount of (gains)/losses reclassified out of accumulated other comprehensive income/(loss) into contractual interest expense (effective portion) [Abstract]
Interest rate swaps			(1,250)	(2,086)	1,157
3.050% (3.079% effective rate) Notes due 2030 [Member]
Derivatives, Fair Value [Line Items]
Principal amount of debt			$ 400,000
Stated interest rate (in hundredths)			3.05%
Scheduled maturity date			Feb. 15, 2030
4.20% (4.234% effective rate) Notes due 2029 [Member]
Derivatives, Fair Value [Line Items]
Principal amount of debt			$ 350,000
Stated interest rate (in hundredths)			4.20%
Scheduled maturity date			Apr. 15, 2029
4.125% (4.271% effective rate) Notes due 2028 [Member]
Derivatives, Fair Value [Line Items]
Principal amount of debt				$ 350,000
Stated interest rate (in hundredths)				4.125%
Scheduled maturity date				Mar. 15, 2028
3.875% (4.038% effective rate) Notes due 2027 [Member]
Derivatives, Fair Value [Line Items]
Principal amount of debt					$ 300,000
Stated interest rate (in hundredths)					3.875%
Scheduled maturity date					Mar. 01, 2027
Forward Starting Swaps [Member]
Derivatives, Fair Value [Line Items]
Amount of borrowings outstanding, subject to swaps			$ 150,000	$ 225,000	$ 150,000	$ 150,000
Underlying treasury rate term (in years)			10 years	10 years	10 years	10 years
Weighted average interest rate under derivative instruments (in hundredths)			1.87%	2.86%	2.44%	1.90%
Gain on forward starting interest rate swaps	$ (6,600)	$ (5,100)		$ 7,000	$ 7,300
Gain on hedge ineffectiveness in interest expense				200
Amount of unrealized gains recognized in accumulated other comprehensive income/(loss) on derivatives (effective portion) [Abstract]
Interest rate swaps	$ (6,600)	$ (5,100)		$ 7,000	7,300
Floating to Fixed Interest Rate Swaps (2017) [Member]
Derivatives, Fair Value [Line Items]
Amount of borrowings outstanding, subject to swaps					$ 50,000
Underlying treasury rate term (in years)					1 month
Weighted average interest rate under derivative instruments (in hundredths)					1.693%
Floating to Fixed Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Amount of borrowings outstanding, subject to swaps			$ 225,000
Underlying treasury rate term (in years)			1 month
Weighted average interest rate under derivative instruments (in hundredths)			1.678%