Investment in Unconsolidated Joint Ventures (Details) (USD $)	12 Months Ended											0 Months Ended					0 Months Ended	12 Months Ended		0 Months Ended				0 Months Ended
	Dec. 31, 2013 sqft Equity_Investment Property	Dec. 31, 2012	Dec. 31, 2011 Property	Mar. 09, 2012 sqft	Feb. 10, 2012	Dec. 31, 2013 PKY CalSTRS Austin, LLC [Member]	Dec. 31, 2012 PKY CalSTRS Austin, LLC [Member]	Dec. 31, 2013 7000 Central Park JV, LLC [Member]	Dec. 31, 2012 7000 Central Park JV, LLC [Member]	Dec. 31, 2013 US Airways Building [Member]	Dec. 31, 2012 US Airways Building [Member]	Dec. 13, 2013 7000 Central Park [Member]	Nov. 05, 2013 7000 Central Park [Member] sqft	Oct. 31, 2013 7000 Central Park [Member]	Jun. 03, 2013 US Airways Building [Member] sqft	Oct. 31, 2013 TPGI [Member]	Jun. 03, 2013 US Airways Building [Member] Property sqft	Dec. 31, 2013 US Airways Building [Member]	Feb. 10, 2014 Subsequent Event [Member] Austin Properties [Member] CalSTRS Joint Venture [Member]	Feb. 10, 2014 Subsequent Event [Member] CalSTRS Joint Venture [Member]	Jan. 24, 2014 Subsequent Event [Member] CalSTRS Joint Venture [Member]	Oct. 31, 2013 Preferred Stock [Member] 7000 Central Park [Member]	Oct. 31, 2013 Common Stock [Member] 7000 Central Park [Member]	Dec. 13, 2013 London Interbank Offered Rate (LIBOR) [Member] 7000 Central Park [Member]	Dec. 13, 2013 One-Month LIBOR [Member] 7000 Central Park [Member]
Schedule of Equity Method Investments [Line Items]
Company's share of the Partner's equity						$ 62,700,000
Excess investment						30,500,000
Number of real estate properties	43		2
Ownership interest acquired (in percent)																	75.00%			60.00%	17.00%
Number of Equity Method Investments	3
Area of real estate property (in square feet)	17,600,000			337,000									415,000		225,000		225,000
Total Purchase Price		898,400,000															41,800,000			24,900,000	41,500,000
Ownership percentage of noncontrolling interest																	25.00%
Mortgage secured for properties in a business acquisition																	3,500,000
Interest rate on mortgage (in percent)					1.50%							1.97%					3.00%
Number of stories in a property acquired																	9
Leased percentage of a property acquisition																	100.00%
Months notice of termination																		12 months
Previously acquired interest percentage													40.00%						40.00%
Investment in unconsolidated joint ventures	151,162,000	0				93,171,000	0	15,490,000	0	42,501,000	0	7,600,000		45,000,000								37,000,000	8,000,000
Percentage of equity interest						50.00%		40.00%		74.58%						50.00%							40.00%
New mortgage loan	$ 3,523,000	$ 0	$ 0									$ 30,000,000
Derivative variable rate basis																								LIBOR	One-Month LIBOR
Derivative basis spread over variable rate																								1.75%	1.80%