Investments in Unconsolidated Joint Ventures - Summary of Financial Information of Unconsolidated Joint Ventures (Details) - 712 Fifth Avenue, 111 Sutter Street, 55 Second Street and 60 Wall Street [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule Of Equity Method Investments [Line Items]
Real estate, net	$ 1,645,769		$ 1,645,769		$ 1,055,240
Intangible assets, net	121,687		121,687		97,658
Other assets	95,341		95,341		84,864
Total assets	1,862,797		1,862,797		1,237,762
Notes and mortgages payable, net	1,192,646		1,192,646		866,079
Intangible liabilities, net	25,610		25,610
Other liabilities	24,580		24,580		15,177
Total liabilities	1,242,836		1,242,836		881,256
Equity	619,961		619,961		356,506
Total liabilities and equity	1,862,797		1,862,797		$ 1,237,762
Rental revenue	39,359	$ 34,088	111,981	$ 102,666
Fee and other income	267	125	617	371
Total revenues	39,626	34,213	112,598	103,037
Operating expenses	17,065	13,090	46,060	38,873
Depreciation and amortization	17,156	11,898	46,166	35,888
Total expenses	34,221	24,988	92,226	74,761
Interest and other income, net	179	192	478	559
Interest and debt expense	(12,673)	(9,820)	(36,046)	(28,209)
Net (loss) income before income taxes	(7,089)	(403)	(15,196)	626
Income tax benefit	2		2
Net (loss) income	$ (7,087)	$ (403)	$ (15,194)	$ 626