ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES - Other liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016
ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES
Supplemental executive retirement plan obligations	$ 21,842				$ 21,478
Unrecognized tax benefits	5,219				5,015
Long-term Insurance accruals	9,531				9,088
Deferred tenant improvement allowances	7,361				7,345
Deferred rent	4,909				5,433
Asset retirement obligations	1,180				1,464
Other	211				894
Total other liabilities	$ 50,253	$ 49,103	$ 48,911	$ 49,316	$ 50,717	$ 53,803	$ 54,925	$ 55,304