SCHEDULE III-Consolidated Real Estate and Accumulated Depreciation Rollforward (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Real estate assets
Balance, beginning of period	$ 1,995,417		$ 1,938,676		$ 1,687,276
Property acquisitions	0		0		270,082
Improvements	154,594	[1]	60,677	[1]	41,303	[1]
Cost of Real Estate Sold	0		0		(57,188)
Other	(13,187)	[1],[2]	(3,936)	[1],[2]	(2,797)	[1],[2]
Balance, end of period	2,136,824		1,995,417		1,938,676
Accumulated depreciation
Balance, beginning of period	318,581		270,494		234,595
Additions-depreciation	55,159	[1]	51,949	[1]	47,792	[1]
Cost of Real Estate Sold	0		0		(9,216)
Other	(12,316)	[1],[2]	(3,862)	[1],[2]	(2,677)	[1],[2]
Balance, end of period	$ 361,424		$ 318,581		$ 270,494

[1] Includes discontinued operations for 160 King Street, which was sold on December 4, 2012.

[2] Other deductions for the years ended December 31, 2014, 2013 and 2012 represent the write-off of fully depreciated assets.