Note 1 - Organization and Formation of the Company (Detail) (USD $)	1 Months Ended	6 Months Ended
	Jul. 31, 1998	Jun. 30, 2012	Dec. 31, 2011	Dec. 30, 1998
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest	12.11%	21.52%
Number of Operating Partnership Units Converted into by Limited Partnership Interests (in Shares)	59,479,633
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	87.89%
Common Stock, Par or Stated Value Per Share (in Dollars per share)		$ 0.001	$ 0.001	$ 0.001
Number of Real Estate Properties		104
Mission West Properties, L.P. [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		25.88%
Mission West Properties, L.P. I [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		21.86%
Mission West Properties, L.P. II [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		16.32%
Mission West Properties, L.P. III [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		12.53%
Mission West Properties, L.P. IV [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		21.86%
Mission West Properties, L.P. V [Member]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		16.32%