Property Transactions (Fair Value of Assets and Liabilities Acquired) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) ft² a	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jul. 19, 2013 USD ($) ft²	Apr. 25, 2013 USD ($) ft²	Feb. 28, 2013 USD ($) ft²
Intangible assets:
Finite-Lived Intangible Asset, Acquired-in-Place Leases	$ 112,937,000	$ 147,360,000
Intangible liabilities:
Proceeds from Equity Method Investment, Dividends or Distributions	8,760,000	10,296,000	$ 67,101,000
Proceeds from Sale of Real Estate Held-for-investment	225,307,000	244,471,000	178,966,000
Outstanding Amount of Mortgage Note Payable of Joint Venture	$ 402,000,000
Spring & 8th/ NCR [Member]
Business Acquisition [Line Items]
Acres of Land Available for Development or Sale | a	4.16
Intangible liabilities:
Total net assets acquired	$ 0
Square footage of real estate property (square feet) | ft²	485,000
816 Congress Austin, TX [Member]
Intangible liabilities:
Total net assets acquired					$ 102,400,000
Square footage of real estate property (square feet) | ft²					435,000
Business Combination, Acquisition Related Costs			342,000
Texas Acquisition [Member]
Intangible liabilities:
Total net assets acquired				$ 1,100,000,000
Business Combination, Acquisition Related Costs			4,200,000
777 Main Fort Worth, TX [Member]
Intangible liabilities:
Square footage of real estate property (square feet) | ft²				980,000
Greenway Plaza Houston, TX [Member]
Intangible liabilities:
Square footage of real estate property (square feet) | ft²				4,300,000.0
Post Oak Central [Member]
Intangible liabilities:
Total net assets acquired						$ 200,000,000
Square footage of real estate property (square feet) | ft²						1,300,000.0
Business Combination, Acquisition Related Costs			231,000
Terminus Two Hundred LLC [Member]
Intangible liabilities:
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property			19,700,000
Term Loan [Member] | Texas Acquisition [Member]
Intangible liabilities:
Gains (Losses) on Extinguishment of Debt			2,600,000
MSREF Terminus Two Hundred LLC [Member] | Terminus Two Hundred LLC [Member]
Intangible liabilities:
Total net assets acquired						$ 53,800,000
Outstanding Amount of Mortgage Note Payable of Joint Venture						74,600,000
Terminus Office Holdings [Member]
Intangible liabilities:
Debt Instrument, Face Amount						$ 82,000,000
Proceeds from Equity Method Investment, Dividends or Distributions			39,200,000
Business Combination, Acquisition Related Costs			122,000
Ownership Percentage of Partner in Joint Venture						50.00%
Proceeds from Sale of Real Estate Held-for-investment			112,200,000
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property			37,100,000
Terminus Two Hundred LLC [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements			25,040,000
Building			101,472,000
Tenant improvements			17,600,000
Business Acquisition Purchase Price Allocation Tangible Assets Other			101,000
Business Acquisition Purchase Price Allocation Deferred Rent Receivable			44,000
Tangible assets			144,257,000
Intangible assets:
Above-market leases			1,512,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			14,355,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease			0
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option			0
Total intangible assets			15,867,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable			0
Intangible liabilities:
Below-market leases			(9,273,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease			0
Business Acquisition Purchase Price Allocation Intangible Liabilities Total			(9,273,000)
Total net assets acquired			150,851,000
816 Congress Austin, TX [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements			6,817,000
Building			86,391,000
Tenant improvements			3,500,000
Business Acquisition Purchase Price Allocation Tangible Assets Other			0
Business Acquisition Purchase Price Allocation Deferred Rent Receivable			0
Tangible assets			96,708,000
Intangible assets:
Above-market leases			89,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			8,222,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease			0
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option			2,403,000
Total intangible assets			10,714,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable			0
Intangible liabilities:
Below-market leases			(2,820,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease			(1,981,000)
Business Acquisition Purchase Price Allocation Intangible Liabilities Total			(4,801,000)
Total net assets acquired			102,621,000
Texas Acquisition [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements			306,563,000
Building			586,150,000
Tenant improvements			114,220,000
Business Acquisition Purchase Price Allocation Tangible Assets Other			0
Business Acquisition Purchase Price Allocation Deferred Rent Receivable			0
Tangible assets			1,006,933,000
Intangible assets:
Above-market leases			4,959,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			117,630,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease			2,958,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option			0
Total intangible assets			125,547,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable			0
Intangible liabilities:
Below-market leases			(47,170,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease			(2,508,000)
Business Acquisition Purchase Price Allocation Intangible Liabilities Total			(49,678,000)
Total net assets acquired			1,082,802,000
Post Oak Central [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements			88,406,000
Building			118,470,000
Tenant improvements			10,877,000
Business Acquisition Purchase Price Allocation Tangible Assets Other			0
Business Acquisition Purchase Price Allocation Deferred Rent Receivable			0
Tangible assets			217,753,000
Intangible assets:
Above-market leases			995,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases			26,968,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease			0
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option			0
Total intangible assets			27,963,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable			0
Intangible liabilities:
Below-market leases			(14,792,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease			0
Business Acquisition Purchase Price Allocation Intangible Liabilities Total			(14,792,000)
Total net assets acquired			$ 230,924,000
Northpark Town Center [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements		24,577,000
Building		274,151,000
Tenant improvements		21,674,000
Business Acquisition Purchase Price Allocation Tangible Assets Other		0
Business Acquisition Purchase Price Allocation Deferred Rent Receivable		0
Tangible assets		320,402,000
Intangible assets:
Above-market leases		2,846,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases		30,159,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease		0
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option		0
Total intangible assets		33,005,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable		0
Intangible liabilities:
Below-market leases		(8,018,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease		0
Business Acquisition Purchase Price Allocation Intangible Liabilities Total		(8,018,000)
Total net assets acquired		345,389,000
Fifth Third Center [Member]
Business acquisition cost of acquired entity purchase price allocation
Land and improvements		22,863,000
Building		163,649,000
Tenant improvements		16,781,000
Business Acquisition Purchase Price Allocation Tangible Assets Other		1,014,000
Business Acquisition Purchase Price Allocation Deferred Rent Receivable		0
Tangible assets		204,307,000
Intangible assets:
Above-market leases		632,000
Finite-Lived Intangible Asset, Acquired-in-Place Leases		17,096,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Below Market Ground Lease		338,000
Business Acquisition Purchase Price Allocation Amortizable Intangible Assets Ground Lease Purchase Option		0
Total intangible assets		18,066,000
Business Acquisition Purchase Price Allocation Tangible Liabilities Accounts Payable		(1,026,000)
Intangible liabilities:
Below-market leases		(9,374,000)
Business Acquisition Purchase Price Allocation Amortizable Intangible Liabilities Above Market Ground Lease		0
Business Acquisition Purchase Price Allocation Intangible Liabilities Total		(9,374,000)
Total net assets acquired		$ 211,973,000