RECENT TRANSACTIONS (Details) $ / shares in Units, $ in Thousands					6 Months Ended
	Jul. 10, 2018 USD ($) a	Jun. 08, 2018 USD ($) a extention_option	Apr. 30, 2018 USD ($) extention_option	Feb. 23, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares
Debt Instrument [Line Items]
Notes receivable, net					$ 4,085	$ 5,864
Repurchase of common shares (in shares) | shares				475,920
Common stock, par value (in dollars per share) | $ / shares				$ 0.01	$ 0.01	$ 0.01
Repurchase price per share (in dollars per share) | $ / shares				$ 120.33
Repurchase of common shares				$ 57,300	$ 57,267
250 Water Street
Debt Instrument [Line Items]
Area of land purchased | a		1
Purchase price of land acquired		$ 180,000
Payments to acquire land		53,100
Wacker110 N | Construction Loans
Debt Instrument [Line Items]
Number of extension options | extention_option			2
Term of extension option			1 year
Loan amount			$ 494,500
Joint venture debt guaranteed			$ 89,000
London Interbank Offered Rate (LIBOR) | Wacker110 N | Construction Loans
Debt Instrument [Line Items]
Interest rate margin (as a percent)			3.00%
Subsequent Event
Debt Instrument [Line Items]
Area of land sold (in acres) | a	123
Sales price of land	$ 69,000
Notes receivable, net	$ 35,800
Notes Payable, Other Payables | 250 Water Street
Debt Instrument [Line Items]
Note payable to acquire land		$ 129,700
Interest free term		6 months
Number of extension options | extention_option		3
Term of extension option		6 months
Interest rate (as a percent)		6.00%
Minimum paydown for term extension		$ 30,000