Leases - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Straight line rent adjustment		$ 32,268
Uncollectible rent receivable	$ 1,842			$ 1,842
Rental and other revenues related to operating lease payments	$ 396,305		$ 385,586	786,265	$ 766,670
Rental and other revenues related to operating lease payments, variable leases				$ 104,605	$ 94,017
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]		well:LeaseRightOfUseAsset				well:LeaseRightOfUseAsset
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	well:LeaseRightOfUseAsset			well:LeaseRightOfUseAsset		well:LeaseRightOfUseAsset
Operating Lease, Liability, Statement of Financial Position [Extensible List]	well:LeaseLiability			well:LeaseLiability		well:LeaseLiability
Finance Lease, Liability, Statement of Financial Position [Extensible List]	well:LeaseLiability			well:LeaseLiability		well:LeaseLiability
Minimum
Lessee, Lease, Description [Line Items]
Lease term extension period				1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease term extension period				25 years