Consolidated Variable Interest Entities (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)
Consolidated Variable Interest Entity [Abstract]
Rentable square feet of office property under development (in sq feet) | ft²	1,200,000
Assets and liabilities of consolidated variable interest entity [Abstract]
Land held for development	$ 137,340	$ 128,248
Prepaid expense and other assets	63,494	28,843
Accounts payable, accrued expenses and other liabilities	$ 257,338	$ 218,922
Consolidated Variable Interest Entity [Member]
Consolidated Variable Interest Entity [Abstract]
Rentable square feet of office property under development (in sq feet) | ft²	150,000
Total anticipated development costs	$ 71,300
Contribution of cash to acquire interest in consolidated joint venture	20,000
Contributions funded to acquire interest in consolidated joint venture	$ 12,800
Interest in consolidated joint venture (in hundredths)	80.00%
Partner's contribution of property to acquire interest in consolidated joint venture	$ 5,000
Partner's interest in consolidated joint venture (in hundredths)	20.00%
Advance to consolidated affiliate	$ 46,300
Assets and liabilities of consolidated variable interest entity [Abstract]
Land held for development	16,565
Prepaid expense and other assets	1,537
Accounts payable, accrued expenses and other liabilities	$ 235
London Interbank Offered Rate (LIBOR) [Member] | Consolidated Variable Interest Entity [Member]
Consolidated Variable Interest Entity [Abstract]
Variable interest rate basis	LIBOR plus 250 basis points
Interest rate, basis spread (in hundredths)	2.50%