Investment in Unconsolidated Joint Ventures - Income Statement of Unconsolidated Joint Ventures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 126,381	[1]	$ 115,747	[1]	$ 110,460	[1]	$ 104,113	[1]	$ 77,465	[1]	$ 73,325	[1]	$ 72,623	[1]	$ 68,165	[1]	$ 456,701		$ 291,579	$ 210,496
Operating expenses	133,253		106,275		103,390		94,160		82,226		73,445		67,047		62,372		437,078		285,091	235,792
Operating income before interest and depreciation and amortization	(6,872)		9,472		7,070		9,953		(4,761)		(120)		5,576		5,793		19,623		6,488	(25,296)
Interest expense	17,515		16,543		16,793		15,244		12,610		11,521		11,162		10,329		66,095		45,622	34,352
Depreciation and amortization																	182,955		118,031	74,626
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Total revenues																	98,482		7,291
Operating expenses																	40,326		2,439
Operating income before interest and depreciation and amortization																	58,156		4,852
Interest expense																	34,288		1,814
Depreciation and amortization																	39,319		3,632
Net income (loss)																	(15,451)		(594)
Equity Method Investee | US Airways Building
Schedule of Equity Method Investments [Line Items]
Total revenues																	4,504		2,560
Operating expenses																	3		0
Operating income before interest and depreciation and amortization																	4,501		2,560
Interest expense																	413		209
Depreciation and amortization																	2,089		1,219
Net income (loss)																	1,999		1,132
Equity Method Investee | 7000 Central Park JV, LLC
Schedule of Equity Method Investments [Line Items]
Total revenues																	7,430		1,136
Operating expenses																	3,856		778
Operating income before interest and depreciation and amortization																	3,574		358
Interest expense																	769		270
Depreciation and amortization																	4,352		836
Net income (loss)																	(1,547)		(748)
Equity Method Investee | PKY CalSTRS Austin, LLC
Schedule of Equity Method Investments [Line Items]
Total revenues																	86,548	[2]	3,595
Operating expenses																	36,467	[2]	1,661
Operating income before interest and depreciation and amortization																	50,081	[2]	1,934
Interest expense																	33,106	[2]	1,335
Depreciation and amortization																	32,878	[2]	1,577
Net income (loss)																	$ (15,903)	[2]	$ (978)

[1] The amounts presented for the three months ended March 31, 2013, June 30, 2013 and September 30, 2013 differ from the amounts previously reported in the Company's Quarterly Reports on Form 10-Q as a result of discontinued operations consisting of properties sold in 2013 or classified as held for sale as of December 31, 2013.

[2] Activity reflected through the date of the joint venture termination on November 16, 2014.