Segment Reporting - Operating Activity Within Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total office revenues	$ 187,333	$ 170,348
Office expenses	(60,356)	(54,885)
Total multifamily revenues	24,914	24,133
Multifamily expenses	(6,698)	(5,947)
Segment profit	145,193	133,649
Office segment
Segment Reporting Information [Line Items]
Total office revenues	187,333	170,348
Office expenses	(60,356)	(54,885)
Segment profit	126,977	115,463
Multifamily segment
Segment Reporting Information [Line Items]
Total multifamily revenues	24,914	24,133
Multifamily expenses	(6,698)	(5,947)
Segment profit	$ 18,216	$ 18,186