Derivative Financial Instruments (Details) - USD ($) $ in Thousands			12 Months Ended
	Aug. 14, 2019	Mar. 07, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Unsecured notes			$ 484,383	$ 708,734
Repayments Of unsecured debt			250,000	150,000	$ 0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax			(15,585)	402	1,151
Amount reclassified from accumulated other comprehensive loss			3,269	5,342	11,103
Interest Expense			151,264	148,456	$ 132,629
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			4,100
Term Loan Due December 2020 [Member]
Derivative [Line Items]
Repayments of interest rate swap breakage fee	$ 1,100
Repayments Of unsecured debt	$ 300,000
Debt Instrument Maturity Period	2020-12
Fair Value, Measurements, Recurring [Member]
Derivative [Line Items]
Interest Rate Cash Flow Hedge Asset at Fair Value			2,987	17,482
Interest Rate Cash Flow Hedge Liability at Fair Value			(1,515)	(5,491)
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative [Line Items]
Interest Rate Cash Flow Hedge Asset at Fair Value			2,987	17,482
Interest Rate Cash Flow Hedge Liability at Fair Value			(1,515)	(5,491)
Interest Rate Cash Flow Hedge Derivative At Fair Value Net			$ 1,472	11,991
Treasury Lock [Member]
Derivative [Line Items]
Derivative, Inception Date			Dec. 06, 2018
Derivative, Maturity Date			Jun. 28, 2019
Derivative, Notional Amount			$ 250,000
Derivative, Description of Variable Rate Basis			30 year U.S. Treasury
Derivative, Fixed Interest Rate		4.65%	3.147%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 0
Interest Rate Cash Flow Hedge Liability at Fair Value				(5,491)
Unsecured notes		$ 300,000
Unsecured notes maturity period		2049-03
Debt Instrument, Term		30 years
Treasury Lock [Member] | Accumulated Other Comprehensive Income (Loss) [Member]
Derivative [Line Items]
Unsecured notes		$ 5,700
Derivative @ 1.824% 300M [Member]
Derivative [Line Items]
Derivative, Inception Date			Apr. 03, 2017
Derivative, Maturity Date			Dec. 02, 2020
Derivative, Notional Amount			$ 300,000
Derivative, Description of Variable Rate Basis			1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			1.824%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 0	3,759
Derivative @ 1.053% 265M [Member]
Derivative [Line Items]
Derivative, Inception Date			Aug. 01, 2016
Derivative, Maturity Date			Jan. 05, 2022
Derivative, Notional Amount			$ 265,000
Derivative, Description of Variable Rate Basis			1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			1.053%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 2,674	10,838
Derivative @ 1.30250% 19.767M [Member]
Derivative [Line Items]
Derivative, Inception Date			Apr. 07, 2016
Derivative, Maturity Date			Apr. 01, 2023
Derivative, Notional Amount			$ 19,767
Derivative, Description of Variable Rate Basis			1 Month LIBOR
Derivative, Fixed Interest Rate			1.303%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 148	880
Derivative @ 1.490% 32.952M [Member]
Derivative [Line Items]
Derivative, Inception Date			Dec. 01, 2016
Derivative, Maturity Date			Nov. 01, 2023
Derivative, Notional Amount			$ 32,952
Derivative, Description of Variable Rate Basis			1 Month LIBOR
Derivative, Fixed Interest Rate			1.49%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 84	1,376
Derivative @ 1.542% 24M [Member]
Derivative [Line Items]
Derivative, Inception Date			Sep. 17, 2019
Derivative, Maturity Date			Mar. 17, 2025
Derivative, Notional Amount			$ 24,000
Derivative, Description of Variable Rate Basis			1 Month LIBOR
Derivative, Fixed Interest Rate			1.542%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 81
Derivative @ 2.366% 37.166M [Member]
Derivative [Line Items]
Derivative, Inception Date			Jun. 02, 2017
Derivative, Maturity Date			Jun. 02, 2027
Derivative, Notional Amount			$ 37,166
Derivative, Description of Variable Rate Basis			1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			2.366%
Interest Rate Cash Flow Hedge Asset at Fair Value				$ 629
Interest Rate Cash Flow Hedge Liability at Fair Value			$ (1,515)
Interest Rate Swap [Member]
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months			$ 4,300