Derivative and Hedging Activities (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
	Jun. 06, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Cash Paid on Hedge	$ (20,400)				$ 0	$ (20,430)
Unrealized Gain (Loss) on Derivatives		$ 0	$ (7,100)		0	(13,000)
Derivative, Cash Received on Hedge				$ 15,900
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net		1,300			1,300
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		$ (300)	400		$ (700)	800
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, Notional Amount			$ 300,000	$ 400,000		$ 300,000
Senior Unsecured Notes [Member] | 3.74% Notes Due 2028 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notes payable, effective interest rate				3.74%			3.74%
Senior Unsecured Notes [Member] | 3.67% Notes Due 2029 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notes payable, effective interest rate			3.67%			3.67%	3.67%