Rental and Other Revenues; Rental Property and Other Expenses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Real Estate Revenue, Net [Abstract]
Contractual rents, net									$ 561,242	$ 513,909	$ 476,684
Straight-line rental income, net									23,909	22,054	21,045
Cost recovery income, net									48,730	45,247	39,112
Lease termination fees									2,311	990	658
Other miscellaneous operating revenues									29,442	22,471	18,372
Real estate revenue, net	$ 167,646	$ 166,269	$ 166,860	$ 164,859	$ 160,126	$ 150,766	$ 148,543	$ 145,236	665,634	604,671	555,871
Future minimum base rents [Abstract]
2017	590,003								590,003
2018	566,742								566,742
2019	505,687								505,687
2020	427,392								427,392
2021	367,053								367,053
Thereafter	1,247,247								1,247,247
Total future minimum base rents	$ 3,704,124								3,704,124
Operating Costs and Expenses [Abstract]
Utilities, insurance and real estate taxes									124,940	117,470	113,226
Maintenance, cleaning and general building									86,221	79,091	74,109
Property management and administrative expenses									12,588	12,446	12,093
Other miscellaneous operating expenses									7,336	6,934	6,456
Rental property and other expenses, net									$ 231,085	$ 215,941	$ 205,884