Summary of Significant Accounting Policies - Organization and Principles of Consolidation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) joint_venture property shares	Dec. 31, 2014 USD ($) shares
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operations Commenced Date	Dec. 31, 1993
Current Fiscal Year End Date	--12-31
General Partners' Capital Account, Units Outstanding | shares	97,212,638	94,108,000
Partners' Capital Account, Units | shares	97,366,808	94,262,000
Number Of Joint Ventures That Grant Each Partner A Right To Dissolve The Real Estate Partnership | joint_venture	5
Maximum Period Of TIme In Which Company Capitalizes Interest Costs	12 months
Tax Basis of Investments, Unrealized Appreciation (Depreciation), Net | $	$ 183,900	$ 129,700
Parent Company [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Parent Company, Ownership Percentage of Outstanding Common Partnership Units of Operating Partnership	99.80%	99.80%
Restricted Cash and Cash Equivalents | $	$ 3,767	$ 8,013
Wholly Owned Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | property	200
Unconsolidated Properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Real Estate Properties | property	118
Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Equity Method Investment, Accretion Period	10 years
Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Equity Method Investment, Accretion Period	40 years
Building and Improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Tenant Improvements [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Furniture and Fixtures [Member] | Minimum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] | Maximum [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property, Plant and Equipment, Useful Life	7 years