ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES - Other liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
ACCRUED EXPENSES, OTHER CURRENT LIABILITIES AND OTHER LIABILITIES
Senior executive retirement plan obligations	$ 22,113				$ 20,696
Unrecognized Tax Benefits	7,605				7,475				$ 4,434	$ 2,105
Deferred tenant improvement allowances	6,289				5,859
Other miscellaneous liabilities	5,156				3,395
Deferred rent	4,712				3,798
Total	$ 45,875	$ 44,150	$ 44,734	$ 42,120	$ 41,223	$ 39,256	$ 37,744	$ 37,257