Derivatives (Details) - USD ($) $ in Thousands			3 Months Ended		9 Months Ended
	Aug. 14, 2019	Mar. 07, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Derivative [Line Items]
Unsecured notes			$ 449,309		$ 449,309		$ 708,734
Repayments of Unsecured Debt					250,000	$ 150,000
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax			(3,851)	$ 2,717	(18,567)	16,511
Amount reclassified from accumulated other comprehensive loss			1,677	1,148	2,085	4,701
Interest Expense			38,253	$ 36,618	113,178	$ 111,477
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months					5,500
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			2,642		2,642		17,482
Interest Rate Cash Flow Hedge Liability at Fair Value			(2,494)		(2,494)		(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			2,642		2,642		17,482
Interest Rate Cash Flow Hedge Liability at Fair Value			(2,494)		(2,494)		(5,491)
Interest Rate Cash Flow Hedge Derivative At Fair Value Net			148		$ 148		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		$ 250,000
Derivative, Description of Variable Rate Basis					30 year U.S. Treasury
Derivative, Fixed Interest Rate		4.65%	3.147%		3.147%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 0		$ 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 $300M Term [Member]
Derivative [Line Items]
Derivative, Inception Date					Apr. 03, 2017
Derivative, Maturity Date					Dec. 02, 2020
Derivative, Notional Amount			$ 300,000		$ 300,000
Derivative, Description of Variable Rate Basis					1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			1.824%		1.824%
Interest Rate Cash Flow Hedge Asset at Fair Value							3,759
Derivatives 200K @ 1.04770% and 65K @ 1.07000% [Member]
Derivative [Line Items]
Derivative, Inception Date					Aug. 01, 2016
Derivative, Maturity Date					Jan. 05, 2022
Derivative, Notional Amount			$ 265,000		$ 265,000
Derivative, Description of Variable Rate Basis					1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			1.053%		1.053%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 2,581		$ 2,581		10,838
Derivative @ 1.30250% 20.0M [Member]
Derivative [Line Items]
Derivative, Inception Date					Apr. 07, 2016
Derivative, Maturity Date					Apr. 01, 2023
Derivative, Notional Amount			$ 19,855		$ 19,855
Derivative, Description of Variable Rate Basis					1 Month LIBOR
Derivative, Fixed Interest Rate			1.303%		1.303%
Interest Rate Cash Flow Hedge Asset at Fair Value			$ 61		$ 61		880
Derivative $33M Swap [Member]
Derivative [Line Items]
Derivative, Inception Date					Dec. 01, 2016
Derivative, Maturity Date					Nov. 01, 2023
Derivative, Notional Amount			$ 33,000		$ 33,000
Derivative, Description of Variable Rate Basis					1 Month LIBOR
Derivative, Fixed Interest Rate			1.49%		1.49%
Interest Rate Cash Flow Hedge Asset at Fair Value							1,376
Interest Rate Cash Flow Hedge Liability at Fair Value			$ (137)		$ (137)
Derivative $24M Swap [Member]
Derivative [Line Items]
Derivative, Inception Date					Sep. 17, 2019
Derivative, Maturity Date					Mar. 17, 2025
Derivative, Notional Amount			$ 24,000		$ 24,000
Derivative, Description of Variable Rate Basis					1 Month LIBOR
Derivative, Fixed Interest Rate			1.542%		1.542%
Interest Rate Cash Flow Hedge Liability at Fair Value			$ (206)		$ (206)
Derivative @ 2.36600% 37.5K [Member]
Derivative [Line Items]
Derivative, Inception Date					Jun. 02, 2017
Derivative, Maturity Date					Jun. 02, 2027
Derivative, Notional Amount			$ 37,309		$ 37,309
Derivative, Description of Variable Rate Basis					1 Month LIBOR with Floor
Derivative, Fixed Interest Rate			2.366%		2.366%
Interest Rate Cash Flow Hedge Asset at Fair Value							$ 629
Interest Rate Cash Flow Hedge Liability at Fair Value			$ (2,151)		$ (2,151)
Swap [Member]
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months					$ 5,900