Share-Based Compensation (Multi-Year Outperformance Plan Agreement) (Details) - USD ($)					3 Months Ended
		Apr. 15, 2016	Apr. 15, 2015	Apr. 15, 2014	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments of distributions					$ 428,000	$ 593,000
New Multi-Year Outperformance Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity-based compensation					$ (6,500,000)	200,000
New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Opp units issued (in shares)				$ 8,880,579
Company's market capitalization percentage				5.00%
Share-based payment award, award vesting rights					33.33%
Shares earned (in shares)			367,059
Distribution entitlement percentage					10.00%
Payments of distributions					$ 100,000	$ 100,000
New Multi-Year Outperformance Plan | Performance Shares | Performance Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Absolute Component: 4% of any excess Total Return if total stockholder return attained above an absolute hurdle measured from the beginning of such period:					21.00%
100% will be earned if total stockholder return achieved is at least:	[1]				18.00%
50% will be earned if total stockholder return achieved is:	[1]				0.00%
0% will be earned if total stockholder return achieved is less than:	[1]				0.00%
New Multi-Year Outperformance Plan | Performance Shares | Annual Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Absolute Component: 4% of any excess Total Return if total stockholder return attained above an absolute hurdle measured from the beginning of such period:					7.00%
100% will be earned if total stockholder return achieved is at least:	[1]				6.00%
50% will be earned if total stockholder return achieved is:	[1]				0.00%
0% will be earned if total stockholder return achieved is less than:	[1]				0.00%
New Multi-Year Outperformance Plan | Performance Shares | Interim Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Absolute Component: 4% of any excess Total Return if total stockholder return attained above an absolute hurdle measured from the beginning of such period:					14.00%
100% will be earned if total stockholder return achieved is at least:	[1]				12.00%
50% will be earned if total stockholder return achieved is:	[1]				0.00%
0% will be earned if total stockholder return achieved is less than:	[1]				0.00%
Relative Component | Excess Return, Above Peer Group | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized, percentage of benchmark					4.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of maximum					100.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Minimum | Performance Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					0.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Minimum | Annual Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					0.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Minimum | Interim Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					0.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Maximum | Performance Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					18.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Maximum | Annual Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					6.00%
Relative Component | Cumulative Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares | Maximum | Interim Period
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Return percentage threshold					12.00%
Relative Component | Cumulative Return, Equal to Threshold | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of maximum					50.00%
Relative Component | Cumulative Return, Below Threshold | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares awarded as a percentage of maximum					0.00%
Absolute Component | Excess Return, Above Threshold | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized, percentage of benchmark					4.00%
Subsequent Event | New Multi-Year Outperformance Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares earned (in shares)		805,679

[1] The “Peer Group” is comprised of certain companies in the SNL US REIT Office Index.