Summary of Significant Accounting Policies and Procedures and Newly Adopted Accounting Standards (Tables)

12 Months Ended

Dec. 31, 2019

Accounting Policies [Abstract]

Schedule of reconciliation of the denominator of the diluted net income per common share computation

The following is a reconciliation of the denominator of the basic net income per common share computation to the denominator of the diluted net income per common share computation.

	2019	2018	2017
Weighted average shares used for the basic net income per share computation	315,837,012	289,427,430	273,465,680
Incremental shares from share-based compensation	322,265	179,532	154,050
Weighted average partnership common units convertible to common shares that were dilutive	—	317,022	317,022
Weighted average shares used for diluted net income per share computation	316,159,277	289,923,984	273,936,752
Unvested shares from share-based compensation that were anti-dilutive	8,113	13,148	32,205
Weighted average partnership common units convertible to common shares that were anti-dilutive	442,073	297,576	88,182

Schedule of estimated useful lives of assets

Properties are depreciated using the straight-line method over the estimated useful lives of the assets.  The estimated useful lives are as follows:

Buildings	25 years or 35 years
Building improvements	4 to 20 years
Tenant improvements and lease commissions	The shorter of the term of the related lease or useful life
Acquired in-place leases	Remaining terms of the respective leases

Schedule of provisions for impairment

The following table summarizes provisions for impairment during the periods indicated below (dollars in millions):

	Year Ended December 31,
	2019		2018		2017
Total provisions for impairment	$	40.2	$	26.3	$	14.8
Number of properties:
Classified as held for sale	9		1		—
Classified as held for investment	5		3		2
Sold	37		40		24