Real Estate Transactions - Sierra Point Towers Acquisition (Details) $ in Millions	1 Months Ended	3 Months Ended
Nov. 30, 2018 USD ($) property	Dec. 31, 2018 USD ($) property	Mar. 31, 2018 USD ($)
Real Estate [Line Items]
Payments to acquire real estate			$ 21
Nonrefundable deposit	$ 15
Life science joint ventures
Real Estate [Line Items]
Number of properties acquired (in properties) \| property	4	2
Payments to acquire real estate	$ 92	$ 245

The cash outflow from the acquisition of a piece of land, anything permanently fixed to it, including buildings, structures on it and so forth; includes real estate intended to generate income for the owner; excludes real estate acquired for use by the owner.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3213-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration